R S AGGARWAL AND V AGGARWAL Solutions for Class 9 Maths Chapter 14 - Areas of Triangles and Quadrilaterals

Page / Exercise

Chapter 14 - Areas of Triangles and Quadrilaterals Exercise MCQ

Question 1

In a ABC it is given that base = 12 cm and height = 5 cm. Its area is

(a) 60 cm2

(b) 30 cm2

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

(d) 45 cm2

Solution 1

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 2

The lengths of three sides of a triangle are 20 cm, 16 cm and 12 cm. The area of the triangle is

(a) 96 cm2

(b) 120 cm2

(c) 144 cm2

(d) 160 cm2

Solution 2

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 3

Each side of an equilateral triangle measures 8 cm. The area of the triangle is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 3

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 4

The base of an isosceles triangle is 8 cm long and each of its equal sides measures 6 cm. The area of the triangle is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 4

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 5

The base of an isosceles triangle is 6 cm and each of its equal sides is 5 cm. The height of triangle is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 5

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 6

Each of the two equal sides of an isosceles right triangle is 10 cm long. Its area is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 6

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 7

Each side of an equilateral triangle is 10 cm long. The height of the triangle is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 7

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 8

The height of an equilateral triangle is 6 cm. Its area is

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 8

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 9

The lengths of the three sides of a triangular field are 40 m, 24 m and 32 m respectively. The area of the triangle is

(a) 480 m2

(b) 320m2

(c) 384 m2

(d) 360m2

Solution 9

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 10

The sides of a triangle are in the ratio 5:12:13 and its perimeter is 150 cm. The area of the triangle is

(a) 375 cm2

(b) 750 cm2

(c) 250 cm2

(d) 500 cm2

Solution 10

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 11

The lengths of the three sides of a triangle are 30 cm, 24 cm and 18 cm respectively. The length of the altitude of the triangle corresponding to the smallest side is

(a) 24 cm

(b) 18 cm

(c) 30 cm

(d) 12 cm

Solution 11

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 12

The base of an isosceles triangle is 16 cm and its area is 48 cm2. The perimeter of the triangle is

(a) 41 cm

(b) 36 cm

(c) 48 cm

(d) 324 cm

Solution 12

 

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 13

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 13

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 14

Each of the equal sides of an isosceles triangle is 13 cm and its base is 24 cm. The area of the triangle is

(a)156 cm2

(b)78 cm2

(c) 60 cm2

(d) 120 cm2

Solution 14

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 15

The base of a right triangle is 48 cm and its hypotenuse is 50 cm long. The area of the triangle is

(a) 168 cm2

(b) 252 cm2

(c) 336 cm2

(d) 504 cm2

Solution 15

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 16

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 16

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Chapter 14 - Areas of Triangles and Quadrilaterals Exercise Ex. 14

Question 1

Find the area of the triangle whose base measures 24 cm and the corresponding height measures 14.5 cm.

Solution 1
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 2

The base of the triangular field is three times its altitude. If the cost of sowing the field at Rs 58 per hectare is Rs 783, find its base and height.

Solution 2
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 3

Find the area of triangle whose sides are 42 cm, 34 cm and 20 cm in length. Hence, find the height corresponding to the longest side.

Solution 3

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals


Question 4

Calculate the area of the triangle whose sides are 18 cm, 24 cm and 30 cm in length. Also, find the length of the altitude corresponding to the smallest side.

Solution 4
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 5

Find the area of a triangular field whose sides are 91m, 98 m, 105m in length. Find the height corresponding to the longest side.

Solution 5

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 6

The sides of a triangle are in the ratio 5: 12:13 and its perimeter is 150 m. Find the area of the triangle.

Solution 6
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 7

The perimeter of a triangular field is 540 m and its sides are in the ratio 25 : 17 : 12. Find the area of the field. Also, find the cost of ploughing the field at Rs. 5 per m2.

Solution 7

It is given that the sides a, b, c of the triangle are in the ratio 25 : 17 : 12,

i.e. a : b : c = 25 : 17 : 12

a = 25x, b = 17x and c = 12x

Given, perimeter = 540 m

25x + 17x + 12x = 540

54x = 540

x = 10

So, the sides of the triangle are

a = 25x = 25(10) = 250 m

b = 17x = 17(10) = 170 m

c = 12x = 12(10) = 120 m

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Cost of ploughing the field = Rs. 5/m2

Cost of ploughing 9000 m2 = Rs. (5 × 9000) = Rs. 45,000

Question 8

Two sides of a triangular field are 85 m and 154 m in length and its perimeter is 324 m. Find (i) the area of the field and (ii) the length of the perpendicular from the opposite vertex on the side measuring 154 m.

Solution 8
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 9

Find the area of an isosceles triangle each of whose equal sides measures 13 cm and whose base measure is 20 cm.

Solution 9
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 10

The base of the isosceles triangle measures 80 cm and its area is 360cm2.Find the perimeter of the triangle.

Solution 10

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 11

The perimeter of an isosceles triangle is 32 cm. The ratio of the equal side to its base is 3 : 2. Find the area of the triangle.

HINT Ratio of sides = 3 : 3 : 2.

* Back answer incorrect

Solution 11

It is given that the ratio of equal side to its base is 3 : 2.

Ratio of sides of isosceles triangle = 3 : 3 : 2

i.e. a : b : c = 3 : 3 : 2

a = 3x, b = 3x and c = 2x

Given, perimeter = 32 cm

3x + 3x + 2x = 32

8x = 32

x = 4

So, the sides of the triangle are

a = 3x = 3(4) = 12 cm

b = 3x = 3(4) = 12 cm

c = 2x = 2(4) = 8 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 12

The perimeter of a triangle is 50 cm. One side of the triangle is 4 cm longer than the smallest side and the third side is 6 cm less than twice the smallest side. Find the area of the triangle.

Solution 12

Let the three sides of a triangle be a, b and c respectively such that c is the smallest side.

Then, we have

a = c + 4

And, b = 2c - 6

Given, perimeter = 50 cm

a + b + c = 50

(c + 4) + (2c - 6) + c = 50

4c - 2 = 50

4c = 52

c = 13

So, the sides of the triangle are

a = c + 4 = 13 + 4 = 17 cm

b = 2c - 6 = 2(13) - 6 = 20 cm

c = 13 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 13

The triangular side walls of a flyover have been used for advertisements. The sides of the walls are 13 m, 14 m, 15 m. The advertisements yield an earning of Rs.2000 per m2 a year. A company hired one of its walls for 6 months. How much rent did it pay?

Solution 13

Three sides of a wall are 13 m, 14 m and 15 m respectively.

i.e.

a = 13 m, b = 14 m and c = 15 m

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Rent for a year = Rs. 2000/m2

Rent for 6 months = Rs. 1000/m2

Thus, total rent paid for 6 months = Rs. (1000 × 84) = Rs. 84,000 

Question 14

The perimeter of the isosceles triangle is 42 cm and its base is R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilateralstimes with each of the equal sides. Find (i) the length of the equal side of the triangle (ii) the area of the triangle (iii)the height of the triangle. (Given, R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals)

Solution 14

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 15

If the area of an equilateral triangle is R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilateralscm2, find its perimeter.

Solution 15
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 16

If the area of an equilateral triangle is R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilateralscm2, find its height.

Solution 16
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 17

Each side of the equilateral triangle measures 8 cm. Find (i) the area of the triangle, correct to 2 places of decimal and (ii) the height of the triangle, correct to 2 places of decimal. Take =1.732.

Solution 17

(i) Area of an equilateral triangle=

Where a is the side of the equilateral triangle

Question 18

The height of an equilateral triangle measures 9 cm. Find its area, correct to 2 places of decimal. Take R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals=1.732.

Solution 18
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

 


Question 19

The base of the right -angled triangle measures 48 cm and its hypotenuse measures 50 cm; find the area of the triangle.

Solution 19
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 20

Find the area of the shaded region in the figure given below.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 20

In right triangle ADB, by Pythagoras theorem,

AB2 = AD2 + BD2 = 122 + 162 = 144 + 256 = 400

AB = 20 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

For ΔABC, 

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, area of shaded region

= Area of ΔABC - Area of ΔABD

= (480 - 96) cm2

= 384 cm2

Question 21

The sides of a quadrilateral ABCD taken in order are 6 cm, 8 cm, 12 cm and 14 cm respectively and the angle between the first two sides is a right angle. Find its area. (Given, R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals)

Solution 21

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Let ABCD be the given quadrilateral such that ABC = 90° and AB = 6 cm, BC = 8 cm, CD = 12 cm and AD = 14 cm.

In ΔABC, by Pythagoras theorem,

AC2 = AB2 + BC2 = 62 + 82 = 36 + 64 = 100

AC = 10 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

In ΔACD, AC = 10 cm, CD = 12 cm and AD = 14 cm

Let a = 10 cm, b = 12 cm and c = 14 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, area of quadrilateral ABCD

= A(ΔABC) + A(ΔACD)

= (24 + 58.8) cm2

= 82.8 cm2

Question 22

Find the perimeter and area of a quadrilateral ABCD in which BC = 12 cm, CD = 9 cm, BD = 15 cm, DA = 17 CM and ABD = 90°.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 22

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

In ΔABD, by Pythagoras theorem,

AB2 = AD2 - BD2 = 172 - 152 = 289 - 225 = 64

AB = 8 cm

Perimeter of quadrilateral ABCD = AB + BC + CD + AD

= 8 + 12 + 9 + 17

= 46 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

In ΔBCD, BC = 12 cm, CD = 9 cm and BD = 15 cm

Let a = 12 cm, b = 9 cm and c = 15 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, area of quadrilateral ABCD

= A(ΔABD) + A(ΔBCD)

= (60 + 54) cm2

= 114 cm2 

Question 23

Find the perimeter and area of the quadrilateral ABCD in which AB = 21 cm, BAC = 90°, AC = 20 cm, CD = 42 cm and AD = 34 cm.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 23

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

In ΔBAC, by Pythagoras theorem,

BC2 = AC2 + AB2 = 202 + 212 = 400 + 441 = 841

BC = 29 cm

Perimeter of quadrilateral ABCD = AB + BC + CD + AD

= 21 + 29 + 42 + 34

= 126 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

In ΔACD, AC = 20 cm, CD = 42 cm and AD = 34 cm

Let a = 20 cm, b = 42 cm and c = 34 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, area of quadrilateral ABCD

= A(ΔABC) + A(ΔACD)

= (210 + 336) cm2

= 546 cm2 

Question 24

Find the area of the quadrilateral ABCD in which BCD is an equilateral triangle, each of whose side is 26 cm, AD=24 cm andR-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals.Also, find the perimeter of the quadrilateral [Given R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals=1.73]

 

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 24

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Perimeter of quad. ABCD = AB + BC + CD + DA = 10 + 26 + 26 + 24 = 86 cm

Question 25

Find the area of a parallelogram ABCD in which AB= 28 cm , BC=26 cm and diagonal AC=30 cm.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 25

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 26

Find the area parallelogram ABCD in which AB=14 cm, BC=10 cm and AC= 16 cm. [Given R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals=1.73]

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 26

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 27

In the given figure ABCD is a quadrilateral in which diagonal BD=64 cm, AL R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals BD and CM R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And QuadrilateralsBD such that AL= 16.8 cm and CM=13.2 cm. Calculate the area of quadrilateral ABCD.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 27

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 28

The area of a trapezium is 475 cm2 and its height is 19 cm. Find the lengths of its two parallel sides if one side is 4 cm greater than the other.

Solution 28

Let the smaller parallel side of trapezium = x cm

Then, larger parallel side = (x + 4) cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, the lengths of two parallel sides are 23 cm and 27 cm respectively.

Question 29

In the given figure, a ΔABC has been given in which AB = 7.5 cm, AC = 6.5 cm and BC = 7 cm. On base BC, a parallelogram DBCE of the same area as that of ΔABC is constructed. Find the height DL of the parallelogram.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 29

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

In ΔABC, AB = 7.5 cm, BC = 7 cm and AC = 6.5 cm

Let a = 7.5 cm, b = 7 cm and c = 6.5 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 30

A field is in the shape of a trapezium having parallel sides 90 m and 30 m. These sides meet the third side at right angles. The length of the fourth side is 100 m. If it costs Rs.5 to plough 1 m2 of the field, find the total cost of ploughing the field.

Solution 30

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Construction: Draw BT CD

In ΔBTC, by Pythagoras theorem,

BT2 = BC2 - CT2 = 1002 - 602 = 10000 - 3600 = 6400

BT = 80 m

AD = BT = 80 m

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Cost of ploughing 1 m2 field = Rs. 5

Cost of ploughing 4800 m2 field = Rs. (5 × 4800) = Rs. 24,000

Question 31

A rectangular plot is given for constructing a house, having a measurement of 40 m long and 15 m in the front. According to the laws, a minimum of 3-m-wide space should be left in the front and back each and 2 m wide space on each of the sides. Find the largest area where house can be constructed.

Solution 31

Length of rectangular plot = 40 m

Width of rectangular plot = 15 m

Keeping 3 m wide space in the front and back,

length of rectangular plot = 40 - 3 - 3 = 34 m

Keeping 2 m wide space on both the sides,

width of rectangular plot = 15 - 2 - 2 = 11 m

Thus, largest area where house can be constructed

= 34 m × 11 m

= 374 m2

Question 32

A rhombus -shaped sheet with perimeter 40 cm and one diagonal 12 cm, is painted on both sides at the rate of Rs.5 per cm2. Find the cost of painting.

Solution 32

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Let ABCD be the rhombus-shaped sheet.

Perimeter = 40 cm

4 × Side = 40 cm

Side = 10 cm

AB = BC = CD = AD = 10 cm

Let diagonal AC = 12 cm

Since diagonals of a rhombus bisect each other at right angles,

AO = OC = 6 cm

In right ΔAOD, by Pythagoras theorem,

OD2 = AD2 - AO2 = 102 - 62 = 100 - 36 = 64

OD = 8 cm

BD = 2 × OD = 2 × 8 = 16 cm

Now,

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Cost of painting = Rs. 5/cm2

Cost of painting rhombus on both sides = Rs. 5 × (96 + 96)

= Rs. 5 × 192

= Rs. 960

Question 33

The difference between the semiperimeter and sides of a ΔABC are 8 cm, 7 cm, and 5 cm respectively. Find the area of the triangle.

Solution 33

Let the sides of a triangle be a, b, c respectively and 's' be its semi-perimeter.

Then, we have

s - a = 8 cm

s - b = 7 cm

s - c = 5 cm

Now, (s - a) + (s - b) + (s - c) = 8 + 7 + 5

3s - (a + b + c) = 20

3s - 2s = 20

s = 20

Thus, we have

a = s - 8 = 20 - 8 = 12 cm

b = s - 7 = 20 - 7 = 13 cm

c = s - 5 = 20 - 5 = 15 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 34

A floral design on a floor is made up of 16 tiles , each triangular in shape having sides 16 cm, 12 cm and 20 cm. Find the cost of polishing the tiles at Re 1 per sq cm.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Solution 34
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 35

An umbrella is made by stitching by 12 triangular pieces of cloth, each measuring ((50 cmx20 cm x50 cm).Find the area of the cloth used in it.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 35
R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals
Question 36

In the given figure, ABCD is a square with diagonal 44 cm. How much paper of each shade is needed to make a kite given in the figure?

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 36

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals In ΔAEF, AE = 20 cm, EF = 14 cm and AF = 20 cm

Let a = 20 cm, b = 14 cm and c = 20 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 37

A rectangular lawn, 75 m by 60 m, has two roads, each road 4 m wide, running through the middle of the lawn, one parallel to length and the other parallel to breadth, as shown in the figure. Find the cost of gravelling the roads at Rs.50 per m2.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Solution 37

For road ABCD, i.e. for rectangle ABCD,

Length = 75 m

Breadth = 4 m

Area of road ABCD = Length × Breadth = 75 m × 4m = 300 m2

For road PQRS, i.e. for rectangle PQRS,

Length = 60 m

Breadth = 4 m

Area of road PQRS = Length × Breadth = 60 m × 4 m = 240 m2

 

For road EFGH, i.e. for square EFGH,

Side = 4 m

Area of road EFGH = (Side)2 = (4)2 = 16 m2

 

Total area of road for gravelling

= Area of road ABCD + Area of road PQRS - Area of road EFGH

= 300 + 240 - 16

= 524 m2

 

Cost of gravelling the road = Rs. 50 per m2

Cost of gravelling 524 m2 road = Rs. (50 × 524) = Rs. 26,200

Question 38

The shape of the cross section of canal is a trapezium. If the canal is 10 m wide at the top, 6 m wide at the bottom and the area of its cross section is 640 m2, find the depth of the canal.

Solution 38

Area of cross section = Area of trapezium = 640 m2

Length of top + Length of bottom

= sum of parallel sides

= 10 m + 6 m

= 16 m

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And QuadrilateralsThus, the depth of the canal is 80 m.

Question 39

Find the area of a trapezium whose parallel sides are 11 m and 25 m long, and the nonparallel sides are 15 m and 13 m long.

Solution 39

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

From C, draw CE DA.

Clearly, ADCE is a parallelogram having AD EC and AE DC such that AD = 13 m and D = 11 m.

AE = DC = 11 m and EC = AD = 13 m

BE = AB - AE = 25 - 11 = 14 m

Thus, in ΔBCE, we have

BC = 15 m, CE = 13 m and BE = 14 m

Let a = 15 m, b = 13 m and c = 14 m

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 40

The difference between the lengths of the parallel sides of a trapezium is 8 cm, the perpendicular distance between these sides is 24 cm and the area of the trapezium is 312 cm2. Find the length of each of the parallel sides.

Solution 40

Let the smaller parallel side = x cm

Then, longer parallel side = (x + 8) cm

Height = 24 cm

Area of trapezium = 312 cm2

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Thus, the lengths of parallel sides are 9 cm and 17 cm respectively.

Question 41

A parallelogram and a rhombus are equal in area. The diagonals of the rhombus measure 120 m and 44 m. If one of the sides of the parallelogram measures 66 m, find its corresponding altitude.

Solution 41

Area of parallelogram = Area of rhombus

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 42

A parallelogram and a square have the same area. If the sides of the square measures 40 m and altitude of the parallelogram measures 25 m, find the length of the corresponding base of the parallelogram.

Solution 42

Area of parallelogram = Area of square

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

Question 43

Find the area of a rhombus one side of which measures 20 cm and one of whose diagonals is 24 cm.

Solution 43

Let ABCD be a rhombus and let diagonals AC and BD intersect each other at point O.

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

We know that diagonals of a rhombus bisect each other at right angles.

Thus, in right-angled ΔAOD, by Pythagoras theorem,

OD2 = AD2 - OA2 = 202 - 122 = 400 - 144 = 256

OD = 16 cm

BD = 2(OD) = 2(16) = 32 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

Question 44

The area of a rhombus is 480 cm2, and one of its diagonals measures 48 cm. Find (i) the length of the other diagonal, (ii) the length of each of its sides, and (iii) its perimeter.

Solution 44

(i) Area of a rhombus = 480 cm2

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals 

(ii) Let diagonal AC = 48 cm and diagonal BD = 20 cm

R-s-aggarwal-and-v-aggarwal Solutions Cbse Class 9 Mathematics Chapter - Areas Of Triangles And Quadrilaterals

We know that diagonals of a rhombus bisect each other at right angles.

Thus, in right-angled ΔAOD, by Pythagoras theorem,

AD2 = OA2 + OD2 = 242 + 102 = 576 + 100 = 676

AD = 26 cm

AD = BC = CD = AD = 26 cm

Thus, the length of each side of rhombus is 26 cm.

 

(iii) Perimeter of a rhombus = 4 × side = 4 × 26 = 104 cm