Probability 1 Short Questions (Question 5, 6, 7 & 8)


Question 5:
A box contains 36 green erasers and a number of red erasers.
If an eraser is picked randomly from the box, the probability of picking a red eraser is 5 8 . Find the number of red erasers.

Solution:

Probability of picking a green eraser = 1 – 5 8 = 3 8

Total number of erasers in the box = 36 × 8 3 = 96

Hence, number of red erasers in the box = 96 – 36 = 60



Question 6:
A box contains blue marbles and green marbles. A marble is picked at random from the box.
The probability of picking a blue marble is 6 11 . If there are 30 green marbles in the box, how many blue marbles are there in the box?

Solution:

Probability of picking a green marble = 1 – 6 11 = 5 11

Total number of marbles in the box = 30 × 11 5 = 66

Hence, number of blue marbles in the box = 66 – 30 = 36 



Question 7:
Table below shows the distribution of a group of 90 pupils attending a penalty kick training programme.

Form Four
Form Five
Girls
33
15
Boys
18
24
A pupil is chosen at random from the group to start the penalty kick training.
What is the probability that a boy from Form Five will be chosen?

Solution:
P (a boy from Form Five)
= 24 90 = 4 15


Question 8:
Diagram below shows some number cards.
 
A card is picked at random. State the probability that a prime number is picked.

Solution:
prime number = {11, 19, 37}
P (a prime number)
= 3 6 = 1 2

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