Ncert mathematics solutions class 9 Solutions for Chapter 15 probability

In a cricket match, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the

probability that she did not hit a boundary.

1500 families with 2 children were selected randomly, and the following data were recorded:

Compute the probability of a family, chosen at random, having 2 girls.

Also, check whether the sum of these probabilities is 1.

1500 families with 2 children were selected randomly, and the following data were recorded:

Compute the probability of a family, chosen at random, having No girl

Also, check whether the sum of these probabilities is 1.

1500 families with 2 children were selected randomly, and the following data were recorded:

Compute the probability of a family, chosen at random, having 1 girl

Also, check whether the sum of these probabilities is 1.

Refer to Example 5, Section 14.4, Chapter 14. Find the probability that a student of the class was

born in August.

. An organisation selected 2400 families at random and surveyed them to determine a relationship

between income level and the number of vehicles in a family. The information gathered is listed

in the table below:

Suppose a family is chosen. Find the probability that the family chosen is

(i) earning ₹10000 – 13000 per month and owning exactly 2 vehicles.

(ii) earning ₹16000 or more per month and owning exactly 1 vehicle.

(iii) earning less than ₹7000 per month and does not own any vehicle.

(iv) earning ₹13000 – 16000 per month and owning more than 2 vehicles.

(v) owning not more than 1 vehicle.

Refer to Table 14.7, Chapter 14.

(i) Find the probability that a student obtained less than 20% in the mathematics test.

(ii) Find the probability that a student obtained marks 60 or above.

Total number of students = 135 + 65 = 200

(i) Number of students who like statistics = 135

∴, the probability that a student likes statistics = \frac{135}{200}=\frac{27}{40}

(ii) Number of students who do not like statistics = 65

∴, the probability that a student does not like statistics =\frac{65}{200}=\frac{13}{40}

Refer to Q.2, Exercise 14.2. What is the empirical probability that an engineer lives:

(i) less than 7 km from her place of work?

(ii) more than or equal to 7 km from her place of work?

(iii) within

1/2km from her place of work?

Activity: Note the frequency of two-wheelers, three-wheelers and four-wheelers going past

during a time interval, in front of your school gate. Find the probability that any one vehicle out

of the total vehicles, you have observed is a two-wheeler.

Activity: Ask all the students in your class to write a 3-digit number. Choose any student from

the room at random. What is the probability that the number written by her/him is divisible by

3? Remember that a number is divisible by 3 if the sum of its digits is divisible by 3.

Eleven bags of wheat flour, each marked 5 kg, actually contained the following weights of flour

(in kg):

4.97 5.05 5.08 5.03 5.00 5.06 5.08 4.98 5.04 5.07 5.00

Find the probability that any of these bags chosen at random contains more than 5 kg of flour.

In Q.5, Exercise 14.2, you were asked to prepare a frequency distribution table, regarding the

concentration of sulphur dioxide in the air in parts per million of a certain city for 30 days. Using

this table, find the probability of the concentration of sulphur dioxide in the interval 0.12-0.16 on

any of these days.

The data obtained for 30 days is as follows:

0.03 0.08 0.08 0.09 0.04 0.17 0.16 0.05 0.02 0.06 0.18 0.20 0.11

0.08 0.12 0.13 0.22 0.07 0.08 0.01 0.10 0.06 0.09 0.18 0.11 0.0

7 0.05 0.07 0.01 0.04

In Q.1, Exercise 14.2, you were asked to prepare a frequency distribution table regarding the

blood groups of 30 students of a class. Use this table to determine the probability that a student

of this class, selected at random, has blood group AB.

The blood groups of 30 students of Class VIII are recorded as follows:

A, B, O, O, AB, O, A, O, B, A, O, B, A, O, O, A, AB, O, A, A, O, O, AB, B, A, O, B, A, B, O