The probability of a man hitting a target is (1/4). If he fires 7 times, what is the probability of his hitting the target at least twice?
Using Bernoulli’s Trial we have,
P(Success=x) = nCx.px.q(n-x)
x=0, 1, 2, ………n and q = (1-p), n =7
p = � q = �
The probability of hitting the target at least twice is = P(2) + P(3) + P(4) + P(5) + P(6) + P(7)
⇒ 1-(P(0) + P(1))
⇒ 1 – (7C0(
)0(
)7 + 7C1(
)1(
)6)
⇒ 1 – (
)( (
)6)
⇒ 
1