Notes
Ncert Solutions
Assignments
Revision sheet
Given below are the
Class 9 Maths Important Questions for Probability
a) Concepts questions
b) Calculation problems
c) Multiple choice questions
d) Long answer questions
e) Fill in the blanks
f) Link type comprehension
Link type comprehension
Question 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
Multiple choice Questions
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
Class 9 Maths
Class 9 Science