Question

An athlete has 75% of winning the race if he is not injured. If he is injured, his probability of winning the race is only 15%. If the total chances of winning is 51%, what is the probability that he gets injured?

Answer 1

X = 'is the athlete injured' (X in {0,1})

Y = 'the athlete wins' (Y in {0,1})

P(Y=1|X=0) = 0.75

P(Y=1|X=1) = 0.15

P(Y=1) = 0.51

We are looking for P(X=1) - P(Y=1) = P(Y=1|X=0)*(1-P(X=1)) + P(Y=1|X=1)*P(X=1)

The above equation should provide you with the answer 0.4!

Explanation: