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# NCERT Solution - Probability Class 9 Notes | EduRev

## Class 9 : NCERT Solution - Probability Class 9 Notes | EduRev

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Class IX  Chapter 15 – Probability
Maths

Exercise 15.1 Question 1:
In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
Find the probability that she did not hit a boundary.
Number of times the batswoman hits a boundary = 6
Total number of balls played = 30
Number of times that the batswoman does not hit a boundary = 30 - 6 = 24

Question 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
Also check whether the sum of these probabilities is 1.
Page 2

Cbse-spot.blogspot.com
1

Class IX  Chapter 15 – Probability
Maths

Exercise 15.1 Question 1:
In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
Find the probability that she did not hit a boundary.
Number of times the batswoman hits a boundary = 6
Total number of balls played = 30
Number of times that the batswoman does not hit a boundary = 30 - 6 = 24

Question 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
Also check whether the sum of these probabilities is 1.
Cbse-spot.blogspot.com
2

Total number of families = 475 + 814 + 211
= 1500
(i) Number of families having 2 girls = 475

In a 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:
( ii )

Number of families having 1 girl = 814

Question 3:
(   iii) Number of families having no girl = 211

Therefore, the sum of all these probabilities is 1.
Page 3

Cbse-spot.blogspot.com
1

Class IX  Chapter 15 – Probability
Maths

Exercise 15.1 Question 1:
In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
Find the probability that she did not hit a boundary.
Number of times the batswoman hits a boundary = 6
Total number of balls played = 30
Number of times that the batswoman does not hit a boundary = 30 - 6 = 24

Question 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
Also check whether the sum of these probabilities is 1.
Cbse-spot.blogspot.com
2

Total number of families = 475 + 814 + 211
= 1500
(i) Number of families having 2 girls = 475

In a 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:
( ii )

Number of families having 1 girl = 814

Question 3:
(   iii) Number of families having no girl = 211

Therefore, the sum of all these probabilities is 1.
Cbse-spot.blogspot.com
3

Find the probability that a student of the class was born in August.

different outcomes:
Outcome
3
Frequency   23   72   77   28
If the three coins are simultaneously tossed again, compute the probability of 2 heads
coming up.
Number of times 2 heads come up = 72
Number of studen ts born in the month of August = 6

Three coins are tossed simultaneously 200 times with the following frequencies of
Total number of students = 40

Question 4:
Page 4

Cbse-spot.blogspot.com
1

Class IX  Chapter 15 – Probability
Maths

Exercise 15.1 Question 1:
In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
Find the probability that she did not hit a boundary.
Number of times the batswoman hits a boundary = 6
Total number of balls played = 30
Number of times that the batswoman does not hit a boundary = 30 - 6 = 24

Question 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
Also check whether the sum of these probabilities is 1.
Cbse-spot.blogspot.com
2

Total number of families = 475 + 814 + 211
= 1500
(i) Number of families having 2 girls = 475

In a 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:
( ii )

Number of families having 1 girl = 814

Question 3:
(   iii) Number of families having no girl = 211

Therefore, the sum of all these probabilities is 1.
Cbse-spot.blogspot.com
3

Find the probability that a student of the class was born in August.

different outcomes:
Outcome
3
Frequency   23   72   77   28
If the three coins are simultaneously tossed again, compute the probability of 2 heads
coming up.
Number of times 2 heads come up = 72
Number of studen ts born in the month of August = 6

Three coins are tossed simultaneously 200 times with the following frequencies of
Total number of students = 40

Question 4:
Cbse-spot.blogspot.com
4

Total number of times the coins were tossed = 200

Question 5:
An organization 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:
Monthly income
(in Rs)
Vehicles per family

0   1   2   Above 2
Less than 7000   10   160   25   0
7000 - 10000   0   305   27   2
10000 - 13000   1   535   29   1
13000 - 16000   2   469   59   25
16000 or more   1   579   82   88
Suppose a family is chosen, find the probability that the family chosen is (i) earning
Rs 10000 - 13000 per month and owning exactly 2 vehicles.
(ii) earning Rs 16000 or more per month and owning exactly 1 vehicle.
(iii) earning less than Rs 7000 per month and does not own any vehicle.
(iv) earning Rs 13000 - 16000 per month and owning more than 2 vehicles.
(v) owning not more than 1 vehicle.
Page 5

Cbse-spot.blogspot.com
1

Class IX  Chapter 15 – Probability
Maths

Exercise 15.1 Question 1:
In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
Find the probability that she did not hit a boundary.
Number of times the batswoman hits a boundary = 6
Total number of balls played = 30
Number of times that the batswoman does not hit a boundary = 30 - 6 = 24

Question 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
Also check whether the sum of these probabilities is 1.
Cbse-spot.blogspot.com
2

Total number of families = 475 + 814 + 211
= 1500
(i) Number of families having 2 girls = 475

In a 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:
( ii )

Number of families having 1 girl = 814

Question 3:
(   iii) Number of families having no girl = 211

Therefore, the sum of all these probabilities is 1.
Cbse-spot.blogspot.com
3

Find the probability that a student of the class was born in August.

different outcomes:
Outcome
3
Frequency   23   72   77   28
If the three coins are simultaneously tossed again, compute the probability of 2 heads
coming up.
Number of times 2 heads come up = 72
Number of studen ts born in the month of August = 6

Three coins are tossed simultaneously 200 times with the following frequencies of
Total number of students = 40

Question 4:
Cbse-spot.blogspot.com
4

Total number of times the coins were tossed = 200

Question 5:
An organization 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:
Monthly income
(in Rs)
Vehicles per family

0   1   2   Above 2
Less than 7000   10   160   25   0
7000 - 10000   0   305   27   2
10000 - 13000   1   535   29   1
13000 - 16000   2   469   59   25
16000 or more   1   579   82   88
Suppose a family is chosen, find the probability that the family chosen is (i) earning
Rs 10000 - 13000 per month and owning exactly 2 vehicles.
(ii) earning Rs 16000 or more per month and owning exactly 1 vehicle.
(iii) earning less than Rs 7000 per month and does not own any vehicle.
(iv) earning Rs 13000 - 16000 per month and owning more than 2 vehicles.
(v) owning not more than 1 vehicle.
Cbse-spot.blogspot.com
5

Number of total families surveyed = 10 + 160 + 25 + 0 + 0 + 305 + 27 + 2 + 1 +
535 + 29 + 1 + 2 + 469 + 59 + 25 + 1 + 579 + 82 + 88 = 2400
(i) Number of families earning Rs 10000 - 13000 per month and owning exactly 2
vehicles = 29
Hence, required probability,
(ii) Number of families earning Rs 16000 or more per month and owning exactly 1
vehicle = 579
Hence, required probability,
(iii) Number of families earning less than Rs 7000 per month and does not own any
vehicle = 10
Hence, required probability,   (iv) Number of families earning Rs 13000
- 16000 per month and owning more than
2 vehicles = 25
Hence, required probability,
(v) Number of families owning not more than 1 vehicle = 10 + 160 + 0 + 305 + 1 +
535 + 2 + 469 + 1 + 579 = 2062
Hence, required probability,
Question 6:
A teacher wanted to analyse the performance of two sections of students in a
mathematics test of 100 marks. Looking at their performances, she found that a few
students got under 20 marks and a few got 70 marks or above. So she decided to
group them into intervals of varying sizes as follows: 0 - 20, 20 - 30… 60 - 70, 70 -
100. Then she formed the following table:
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