Four candidates A, B, C, D have applied for the assignment to coach a school cricket team. If A is twice as likely to be selected as B, and B and C are given about the same chance of being selected, while C is twice as likely to be selected as D, what are the probabilities that
(a) C will be selected?
(b) A will not be selected?
Given:
A is twice likely to be selected as B, P(A) = 2 P(B)
& C is twice likely to be selected as D, P(C) = 2 P(D)
It is given that B & C have about the same chance
Thus, P(B) = P(C)
Now, sum of all probabilities is 1,
Thus,
P(A) + P(B) + P(C) + P(D) = 1
P(A) + P(B) + P(B) + P(D) = 1
Thus,
P(A) + P(A)/2 + P(A)/2 + P(C)/2 = 1
[2 P(A) + P(A) + P(A) + P(B)] /2 = 1
4 P(A) + P(A) / 2 = 2
[8 P(A) + P(A)] / 2 = 2
9 P(A) = 4
P(A) = 4/9
Now, (a) P (C will be selected) = P (C)
= P (B)
= 4/9 x ½
= 2/9
(b) P (A will not be selected) = P (A’)
= 1 – P (A) ……. (by complement rule)
= 1 – 4/9
= 9-4/ 9
= 5 / 9