Originally Posted by

**mathwiz2006** I am having difficulty trying to get correct answer for the following problem:

Mr. Smith has 8 master keys that unlock several chests. Only one master key will unlock a given chest. 40% of these chests are usually left open, what is the probability that Mr. Smith can unlock a specific chest if he selects 3 master keys at random?

My attempt: I have a feeling this maybe totally wrong.

I am pretty sure it is a binomial distribution problem

P(X=3) = (8C3)(.4^3)(.6^5) = 3.66176