Given below are the Class 9 Maths Important Questions for Probability
a) Concepts questionsQuestion 1
Twenty four people had a blood test and the results are shown below.
A , B , B , AB , AB , B , O , O , AB , O , B , A
AB , A , O , O , AB , B , O , A , AB , O , B , A
(a) Construct a frequency distribution for the data.
(b) If a person is selected randomly from the group of twenty four people, what is the probability that his/her blood type is not O?
Solution
(a)
class 
frequency 
A 
5 
B 
6 
AB 
6 
O 
7 
(b)
1  (7/24) = 17/24 = 0.71 (rounded to 2 decimal places)
Question 2
Over the past 100 working days, the number of defective bulbs produced by a machine is given in the following table:
No of Defective parts 
0 
1 
2 
3 
Days 
20 
40 
12 
28 
a) The probability that tomorrow output will be defect free is .2
b) The probability that tomorrow output will have at least 1 defect is .8
c) The probability that tomorrow output will have more then 2 defect is .30
d) The probability that tomorrow output will have 3 defects is .28
Solution
a) True P=20/100=.2
b) True , P=(40+12+28)/100=.8
c) False ,P=28/100=.28
d) True. P=28/100=.28
Question 3
The probability of the events lies between
a) 1 ≤ p ≤ 1
b) 0 ≤ p ≤ 1
c) 1 ≤ p ≤ 0
d) 1 < p ≤ 1
Solution (b)
Question 4
Twelve 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 5.12
Find the probability that any of these bags chosen at random contains more than 5 kg
of flour
a) 1/12
b) 7/12
c) 3/4
d) None of these
Solution (b)
No of bags having weight more than 5 kg=7
Total =12
So p=7/12
Question 5
A company selected 4000 households at random and surveyed them to find out a relationship between income level and the number of mobile sets in a home. The information so obtained is listed in the following table:
Monthly income 
No of Mobile sets 

0 
1 
2 
Above 2 

< 10000 
20 
80 
10 
0 
10000  14999 
10 
240 
60 
0 
15000  19999 
0 
380 
120 
30 
20000  24999 
0 
520 
370 
80 
25000 and above 
0 
1100 
760 
220 
Find the probability of a household earning Rs 10000 – Rs 14999 per year and having exactly one mobile set
a) .06
b) .08
c) .04
d) None of these
Solution (a)
Around 240 household are there satisfying the condition
So p=240/4000=.06
Question 6
In the above question, Find the probability of a household earning more than 25000 per year and having exactly 2 mobile set
a) .2
b) .19
c) .12
d) .3
Solution (b)
Around 760 household are there satisfying the condition
So p=760/4000=.19
Question 7
In the above question, find the probability of a household earning more than 25000 per year and having 2 or more mobile set
a) .245
b) .3
c) .1
d) None of these
Solution (a)
Around 980 household are there satisfying the condition
So p=980/4000=.245
Question 8
In the above question, Find the probability of a household having no mobile set at all?
a) 3/400
b) 1/400
c) 1/200
d) None of these
Solution (a)
Around 30 household are there satisfying the condition
So p=30/4000=3/4000
Question 9
In the above question, Find the probability of a household having 3 mobile set and having income less than 10000
a) .1
b) 0
c) .24
d) None of these
Solution (b)
As no household exists like than, So probability is 0