# A sign on the gas pump of a certain chain of gasoline stations encourages customers to have their oil checked, claiming that one out of every four cars should have its oil topped up. What is the probability that exactly 3 of the next 10 cars entering a station should have their oil topped up?

You can use the binomial probability function for these kinds of problems.

The function is this:

P(x) = (nCx)(p^x)[q^(n-x)]

From your problem, n = 10, x = 3, p = 1/4 or .25, q = .75 (q = 1 - p).

Setting up:

P(3) = (10C3)(.25^3)(.75^7)

Can you take it from here to finish?