(1) P(两个球都是黄球) = P(1黄)P(2黄) = 1/3 * 1/2 = 1/6
(2) P(一个白球一个黄球) = P(1白)P(2黄) + P(1黄)P(2白) = 2/3 * 1/2 + 1/3 * 1/2 = 1/2.