Q 1. A die is thrown once, and a
number is noted. The probability that it is a number between and including 1
and 6 is

Solution

Possible outcomes when a
die is thrown once are 1, 2, 3, 4, 5, 6 .
According to the question, the possible outcomes of an event are equal to the
possible outcomes of an experiment.
Hence, the required probability is 1.

Q 2. The probability of an
event occurring is 55%. So, the probability of an event is

Solution

The probability of an
event occurring is 55%. So, the probability of an event is 55/100 = 0.55.

Q 3. In a medical examination
of students of a class, the following blood groups are recorded:

Blood Group
A
AB
B
O
Number of students
10
13
12
5

A student is selected at
random from the class. The probability that he/she has blood group B is

Solution

Total number of students =
10 + 13 + 12 + 5 = 40
The number of students whose blood group is B is 12.
Required probability =

Q 4. The probability of an
impossible event is

Solution

The probability of an
impossible event is 0.

Q 5. An experiment is performed and the
probability of an event A is recorded. So, the probability of event A cannot
be

Solution

The probability of an event cannot be negative.

Q 6. An _____ is an activity which involves the chance or probability of
getting a result.

Solution

An experiment is an activity which involves the chance or probability
of getting a result.

Q 7. If the events A, B and C
are the possible events of an experiment and their probabilities are recorded,
then mark the possible correct answers.

Solution

P(A) + P(B) + P(C) = 0.1 +
0.4 + 0.5 = 1

Sum of the probabilities
of possible events is always 1.

Q 8. Probability represents

Solution

Probability represents the numerical measure of uncertainty.

Q 9. A class has x girls and y
boys. If a student is selected at random, then the probability of selecting a
girl is

Solution

A class has x girls and y
boys. If a student is selected at random, then the probability of selecting a
girl is

Q 10. In 2011, during the rainy season of 90 days,
it was observed that it rained for 20 days only. The probability that it
rained is

Solution

In 2011, during the rainy
season of 90 days, it was observed that it rained for 20 days only. The
probability that it rained is .

Q 11. The probability of an
event occurring is 45%. So, the probability of an event is

Solution

The probability of an
event occurring is 45%. So, the probability of an event is 45/100 = 0.45.

Q 12. The result coming out of the activity or
experiment is called the

Solution

The result coming out of the activity or experiment is called the
outcome.

Q 13. The probability of selecting a boy in a
class is 0.6. If there are 45 students in a class, then the number of girls
in the class is

Solution

According to the question,
Probability = Number of boys / Total number of students in a class

0.6 = Number of boys / 45

Number of boys = 0.6 × 45
= 27

Number of girls = 45 - 27
= 18

Q 14. Two coins are tossed simultaneously 100
times, and we get the following outcomes:
No head = 30, one head = 20 and two heads =
50
Find the probability of getting two heads.

Solution

The number of two heads =
50.
The required probability =

Q 15. Three coins are tossed
simultaneously 200 times with the following frequencies of different outcomes:

Outcome
3 heads
2 heads
1 head
No head
Frequency
23
72
77
28

What is the probability of
2 heads coming up?

Solution

Total number of coins
tossed = 200
Frequency of getting 2 heads coming up = 72
Required probability =

Q 16. In an experiment, the probability of an
event is better approximated when an experiment is performed

Solution

In an experiment, the probability of an event is better approximated
when an experiment is performed a large number of times.

Q 17. In a class of 50 students,
there are 120% boys. So, the number of boys in the class is

Solution

The maximum percentage is
100%. 120% is not valid.

Q 18. If a die is thrown, then
what is the probability of getting an even prime number?

Solution

Possible outcomes in an
experiment are 1, 2, 3, 4, 5, 6 .
Even prime number is 2.
Required probability =

Q 19. A coin is tossed 1000
times. If the probability of getting a tail is 3/8, then how many times is a head
obtained?

Solution

According to the question,
The number of times a tail is obtained = 3/8 × 1000 = 375
The number of times a head is obtained = 1000 - 375 = 625

Q 20. If two coins are tossed
simultaneously, then the probability of getting two tails is

Solution

Possible outcomes when two
coins are tossed: HH, HT, TH, TT, i.e. 4.

The number of outcomes in
an event is 1.

So, the required
probability is .