tejal777 wrote:

x,y and z each try independantly to solv a problem.If their individual probabilities for success are 1/4,1/2 and 5/8 resp.,what is the probability that x and y but not z will solve the problem?

Guys this is my approach where am I going wrong?

Z does not solve the problem=only X solves it+ only Y solves it + both x and Y solve it.

=1/4+1/2+1/4*1/2

=1/4+1/2+1/8

=7/8...which is the wrong ans...

you have answered to the question .

"What is the probability of x OR y solving the problem?"

you must include z's probability of not solving that is (1-5/8) = 3/8

1/4 * 1/2 * 3/8 = 3/64, is this is the answer?