# Class 9 Maths Important Questions for Probability

Given below are the Class 9 Maths Important Questions for Probability
a. Concepts questions
b. Calculation problems
c. Multiple choice questions
e. Fill in the blanks

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)

(b)
$1 - \frac {7}{24} = \frac {17}{24} = 0.71$ (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:

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= $\frac {20}{100}=.2$
b. True  , P= $\frac {(40+12+28)}{100}=.8$
c. False ,P= $\frac {28}{100}=.28$
d. True. P= $\frac {28}{100}=.28$

## 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. $\frac {1}{12}$
b. $\frac {7}{12}$
c. $\frac {2}{3}$
d. None of these
Solution (c)
No of bags having weight more than 5 kg=8
Total =12
So $P= \frac {8}{12} = \frac {2}{3}$

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:

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 $P= \frac {240}{4000}=.06$

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 $P= \frac {760}{4000}=.19$

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 $P= \frac {980}{4000}=.245$

Question 8
In the above question, Find the probability of a household having no mobile set at all?
a. $\frac {3}{400}$
b. $\frac {1}{400}$
c. $\frac {1}{200}$
d. None of these
Solution (a)
Around 30 household are there satisfying the condition
So $P= \frac {30}{4000}= \frac {3}{400}$

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