Question

A fish take contains 16 goldfish and 24 guppies. If you randomly select 2 fish, what is the probability that they are both goldfish

Answer 1

The probability of drawing a goldfish on the first draw is 16 / ( 16 + 24 ), or 16/40, or 2/5. Supposing that the first fish drawn is actually a goldfish, then there are 15 goldfish left among 39 fish, and the probability of drawing a goldfish on the 2nd draw is 15/39, or 5/13. The (joint) probability of drawing 2 goldfish on the 1st 2 draws, without replacement, is (5/13)(2/5) = 2/13.