1. An urn contains seven green balls and five white balls. A sample of three balls is selected at random from the urn. Find the probability that
(a) Only green balls are selected.
(b) At least one white ball is selected.
2. An urn contains six green balls and seven white balls. A sample of four balls is selected at random from the urn. Find the probability that
(a) The four balls have the same color.
(b) The sample contains more green balls than white balls?