Ask a Doubt
Request a call back

Join NOW to get access to exclusive study material for best results

ICSE Class 10 Answered

How many terms of the A P 17,15,13,11..... must be added to get the sum 72?
Asked by suneelmsc | 29 Jun, 2020, 04:59: PM
answered-by-expert Expert Answer
In this AP, we are given a = 17, d = -2, Sn = 72 and we have to find n
Sum of first n terms = n/2[2a+(n-1)d]
Sum is given as 72
72 = n/2[2 x 17 + (n - 1)(-2)]
144 = n[34-2n+2]
144 = n[36-2n]
72 = n(18 - n)
n2 - 18n + 72 = 0
n2 - 12n - 6n + 72 = 0
n(n - 12) - 6(n - 12) = 0
(n - 12)(n - 6) = 0
=> n = 6, 12
Both values of n, being positive integers are valid. We get double answer because sum of 7th to 12th terms is zero, as some terms are positive and some are negative
Answered by Renu Varma | 29 Jun, 2020, 08:05: PM

Application Videos

Concept Videos

Multiple Choice Questions Practice Test
Answered Unanswered My Questions My Answers
ICSE 10 - Maths
the sum n terms of the series root2+root8+ root 18+root 32
Asked by srilakshmivytla28 | 10 Sep, 2023, 09:19: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
The 5th and 9th terms of an arithmetic progression are 4 and -12 respectively. Find (a) the first term (b) common difference (c) sum of 16 terms of the AP
Asked by varma.renu9481 | 13 Mar, 2023, 11:46: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
When do we use s=n/2(a+l) formula and when do we use s=n/2 x {2a+(n-1)d} formula in the sum of a.p?
Asked by rashikulkarni28 | 14 Aug, 2022, 04:32: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
In arithmetic progression , when we use s=n/2 [2a+(n-1)d] then why use a=(n-1)d formula?
Asked by rashikulkarni28 | 14 Aug, 2022, 04:30: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
Given 1/(1*2*3)+1/(2*3*4)+.....+1/(98*99*100)=a/b. Find (b-a).
Asked by arpitadas4117 | 17 Jan, 2022, 02:13: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
mrs gupta replace her total lone of 1,18000 by paying instalments every month. if the instalment for first month is 1000 and it increase by 100 every month ? what amount of lone she still has to pay after the 30 th instalment
Asked by preeti31122005 | 14 Aug, 2021, 01:08: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
the sum of first 6 terms of an A.P is 63 .The ratio of the 10th term to the 20th term is 1:2 . calculate the first and the 15th terms
Asked by savithakotari962 | 08 Feb, 2021, 08:40: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
  The algebraic expression of a sequence is 81-8n. What is 10th term What is the sum of 1st 10 terms whether the sum of any number of terms of the sequence will be 400? Why?
Asked by stehyeapen | 19 Oct, 2020, 01:11: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
The sum of n natural number is 5n2 - 4n, find its 8th term
Asked by ruchitripathi96167 | 22 Sep, 2020, 12:16: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
ICSE 10 - Maths
Find the sum of all even numbers between 10 and 100.
Asked by suneelmsc | 29 Jun, 2020, 05:00: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
My Class Videos Tests ₹ Plans Ask a Doubt
Get Latest Study Material for Academic year 24-25 Click here
×