I need help with this question:

A student is writing a multiple choice quiz consisting of three questions, each having four choices and one correct answer each.

(a)what is the chance that the student will get a perfect score by guessing?

I think this should be $\displaystyle \frac{1}{4}*\frac{1}{4}*\frac{1}{4}=\frac{1}{64}$

(b) what is the change that the student will get at least one question correct by guessing

I'm not sure how to tackle this part. How do I calculate at least one right answer?