For example, there are 10 balls in a bag, including 3 white balls and 7 red balls. Now touch the ball twice, don't put it back, one at a time.

There are two situations in the first question. The first time is a white ball, and the second time is also a white ball. The probability is115. The first time is a red ball, and the second time is a white ball, with a probability of 3/ 10.

Second question, the probability of taking the white ball for the second time is 3/ 10, and the probability of taking the white ball for both times is115, so the probability is p = (115)/(3//kloc-0).