NCERT Solution - Probability Class 9 Notes | EduRev

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

 Page 1


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.   
Answer:   
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.   
Answer:   
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 
  
Answer:   
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.   
Answer:   
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 
  
Answer:   
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.   
   
Answer:   
 
different outcomes:   
Outcome   
3 
heads   
2 heads   1 head   No head  
Frequency   23   72   77   28   
If the three coins are simultaneously tossed again, compute the probability of 2 heads 
coming up.   
Answer:   
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.   
Answer:   
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 
  
Answer:   
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.   
   
Answer:   
 
different outcomes:   
Outcome   
3 
heads   
2 heads   1 head   No head  
Frequency   23   72   77   28   
If the three coins are simultaneously tossed again, compute the probability of 2 heads 
coming up.   
Answer:   
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.   
Answer:   
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.   
Answer:   
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 
  
Answer:   
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.   
   
Answer:   
 
different outcomes:   
Outcome   
3 
heads   
2 heads   1 head   No head  
Frequency   23   72   77   28   
If the three coins are simultaneously tossed again, compute the probability of 2 heads 
coming up.   
Answer:   
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.   
Answer:   
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:   
Read More
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