Compute probability in urn with green returns

An urn contains 5 red, 5 blue, and 5 green balls. You repeatedly draw one ball uniformly at random. If the ball is green, immediately return it to the urn and continue; if it is red or blue, keep it. Stop once you are holding three balls (i.e., three non-green balls). 1) What is the probability that at least two of the three held balls are red? 2) Now suppose the urn instead has 10 red, 5 blue, and 5 green balls (same process). First give an intuitive estimate, then compute the exact probability that at least two of the three held balls are red.