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
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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.
Answer :
Total number of families = 475 + 814 + 211
= 1500
(i) Number of families having 2 girls = 475
(ii) Number of families having 1 girl = 814
(iii) Number of families having no girl = 211
Therefore, the sum of all these probabilities is 1.
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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:
Find the probability that a student of the class was born in August.
Answer :
Three coins are tossed simultaneously 200 times with the following frequencies of 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 :
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 
160 
Answer :
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:
Marks 
Number of student 
0  20 20  30 30  40 40  50 50  60 60  70 70  above 
7 10 10 20 20 15 8 
Total 
90 
(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.
Answer :
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.
Opinion 
Number of students 
like dislike 
135 65 
Find the probability that a student chosen at random
(i) likes statistics, (ii) does not like it
Answer :
The distance (in km) of 40 engineers from their residence to their place of work were found as follows.
5 
3 
10 
20 
25 
11 
13 
7 
12 
31 
19 
10 
12 
17 
18 
11 
32 
17 
16 
2 
7 
9 
7 
8 
3 
5 
12 
15 
18 
3 
12 
14 
2 
9 
6 
15 
15 
7 
6 
12 
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 km from her place of work?
Answer :
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 :
Concentration of SO_{2} (in ppm) 
Number of days (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 
Total 
30 
The above frequency distribution table represents 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.
Answer :
Blood group 
Number of students 
A 
9 
B 
6 
AB 
3 
O 
12 
Total 
30 
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 :
Maths : CBSE NCERT Exercise Solutions for Class 9th for Probability ( Exercise 15.1 ) will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.