the question I have is...

there are:

21 yellow jelly beans
30 green jelly beans
36 red jelly beans
87 total jelly beans

what is the probability that at least 1 is yellow?

I don't know what to do here. I tried doing 1-p(not yellow) but its not giving me the right answer.

any help would be great!

You did not state how many are being drawn. With replacement or without replacement?