Yes you need to use formula from the definition of conditional probability, and you already calculated the denominator. The numerator is easy to be simplified if you can recognize one set is the subset of another.

i.e. For any 2 sets ,

and subsequently it can help you to simplify the intersection in numerator.

Thank you. I was able to get the correct answer to be .01/.59 = .0169. However, I do not understand why it is the correct answer. Why does P(A1 ∩ A2 ∩ A3 | A1 ∪ A2 ∪ A3) = P(A1 ∩ A2 ∩ A3) / P(A1 ∪ A2 ∪ A3)?

Even if I see P(A | B) = P(A ∩ B) / P(B), I still don't fully understand.