A player's batting average in softball is .400. What is the probability he gets 3 hits in his next 5 at-bats?

1 Answer
Jan 28, 2017

The probability is exactly 23.04%23.04%.

Explanation:

This question calls for our old friend the Binomial distribution.

If we let HH be the number of hits in the next 5 at-bats, and we assume each at-bat is independent, then HH has a Binomial distribution with n=5n=5 and p=0.4p=0.4.

Why? Because the probability of a hit on a single at-bat is 0.4, and if the player gets hh hits out of 5 tries, the number of sequences that produce those hh hits is ""_5C_h5Ch.

So we have H ~ "Bin"(n=5, p=0.4).

From there, we just plug the given values for n, p, and h into the binomial formula to get

P(H=h)=""_5C_h (0.4)^h(1-0.4)^(5-h)
P(H=3)=""_5C_3 (0.4)^3(0.6)^(5-3)
color(white)(P(H=3))=10 xx (0.4)^3(0.6)^2
color(white)(P(H=3))=10 xx 0.064 xx 0.36
color(white)(P(H=3))=0.2304

So the probability of getting exactly 3 hits out of the next 5 at-bats is

P(H=3)=0.2304" "=" "23.04%.