only applies for one marble being drawn.
as you are looking two marbles being drawn with replacement maybe could be a better answer?
Ok this question been giving me problems and I've got it wrong 2 times already. It says the urn contains 40 marbles: 12 were white, 18 were red, and 10 were blue. One marble was drawn and then put back. Then a second marble was drawn. What is the probability that both marbles were blue? I looked in my text book and tried to go off what was in there. I came up with 10/40 reduced to 1/4 but that wasn't right if someone can help and let me know were I'm going wrong I'd gladly appreciate it. thanks