CBSE Class 9 Mathematics Probability Set B

Question : 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 : 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:

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:
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 : To know the opinion of the students about the subject statistics, a survey of 200 students was conducted. The data is recorded in the following table.

Find the probability that a student chosen at random (i) likes statistics, (ii) does not like it
Answer:

Question : 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.
Answer:
Number of total bags = 11
Number of bags containing more than 5 kg of flour = 7

Hence, required probability, P = 7/11

Question :

The above frequency distribution table represents 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.
Answer:
Number of students having blood group AB = 3
Total number of students = 30
Hence, required probability, P = 3/10 =1/3

Probability

Q 1 A coin is tossed 100 times. It is observed that 60 times head comes up and 40 times tail comes up then find the probability that neither a head nor a tail comes up.

Q 2 A coin is tossed 100 times with the following frequencies:
Head: 45, tail: 55.
Compute the probability for each event.

Q 3 The percentage of marks obtained by a student in monthly unit tests is given below:
Unit test       I  II   III  IV  V
Percentage 69  71 73  68  76
Find the probability that the student gets more than 68% 

Q 4 A die is thrown 200 times with the following frequency, for the outcomes 1,2,3,4,5,6 , as given below:
Outcomes :  1    2   3     4    5   6
Frequency: 30  40   50  20  30 30
Find the probability that the outcome is less than 5. 

Q 5 1000 families with 2 children were selected randomly and the following data was recorded:
Number of girls in a family:         0       1     2
Number of families :                 200   500   300
If a family is chosen at random, compute the probability that it has
1. no girl, 2. at least one girl. 

Q 6 To know the opinion of students about mathematics, a survey of 100 students was conducted. The data is recorded in the following table:
Opinion:                   Like    Dislike
Number of Students: 70      30

Find the probability that a student chosen at random
1. likes mathematics,
2. dislikes mathematics. 

Please refer to attached file for CBSE Class 9 Mathematics Probability Set B