Question

There is one error in one of five blocks of a program. To find the error, we test three randomly selected blocks. Let X be the number of errors in these three blocks. Compute E(X) and Var(X)

Answer 1

Probability(error in one block)= 1/5
Probability(error in 3 blocks)= 3*(1/5)= 0.6

Let,
0 = No error
1 = error
Hence.
E(x) = 0.4 x 0 x+0.6 + 1
= 1.6