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Three men, P, Q and R aim at a target, the probabilities tha...

Three men, P, Q and R aim at a target, the probabilities that P, Q and R hit the target are 12, 13 and 34 respectively. Find the probability that exactly 2 of them hit the target.

A.

1

B.

12

C.

512

D.

112

Correct answer is C

p(P)=12,p(P)=12

p(Q)=13,p(Q)=23

p(R)=34,p(R)=14

p(exactly two hit the target) = p(P and Q and R') + p(P and R and Q') + p(Q and R and P')

= (12×13×14)+(12×34×23)+(13×34×12)

= 124+624+324

= 512