# Probability| NCERT Solutions| Class 9

NCERT Solutions of  Chapter: Probability. NCERT Solutions along with worksheets and notes for Class 9.

Exercise 15.1

(1) 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.

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

 Number of girls in a family 2 1 0 Number of families 475 814 211

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

(i) 2 girls    (ii) 1 girl    (iii) No girl

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(3) Refer to Example 5, section 14.4, chapter 14. Find the probability that a student of the class was born in August.

Example 5

Ina particular section of class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained:

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(4) Three coins are tossed simultaneously 200 times with the following frequencies of different outcomes:

If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up.

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(6) 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.

Table 14. 7, Chapter 14

 Marks Number of Students 0 – 20 7 20 – 30 10 30 – 40 10 40 – 50 20 50 – 60 20 60 – 70 15 70 – above 8 Total                   90

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(7) To know the option of the students about the subject statistics, a survey of 200 students was conducted. The data is recorded in the following table.

 Opinion Number of students Like 135 Dislike 65

Find the probability that a student chosen at random

(i) likes statistics,

(ii) does not like it.

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(9) 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 two – wheeler.

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(10)  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?

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(11)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.

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(12) 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.

Q 5, Exercise 14.2

A study was conducted to find out the concentration of sulphur dioxide in the air in parts per million (ppm) of a certain city. 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      0.07       0.05     0.07      0.01       0.04

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The frequency distribution table of Q5, exercise 14.2 is given below-

 Concentration of sulphur dioxide (in ppm) Frequency 0.00 – 0.04 4 0.04 – 0.08 9 0.08 – 0.12 9 0.12 – 0.16 2 0.16 – 0.20 4 0.20 – 0.24 2

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Helping Topics

Probability

Worksheet Class 9