Please, partner, draw lots and send.

Someone has answered it step by step, so I'll put it in a more popular way.

Divide the required items into several steps, such as drawing lots twice, one step at a time. Generally speaking, you have to do an operation every time, or multiply or add.

If the first situation analyzed in each step before this step is likely to be established in this step, then multiplication is used. If some situations are possible and some are impossible, then discuss them in categories.

For example, two people draw lots from the 10 branch to find the probability that the second person can't draw the number 2. The first step is the first person to draw, so there are 10 kinds. In the second step, there are 9 kinds, but obviously the first situation in the first step is not all true at this time. Only the first person can draw No.2, and the second person can draw 9 kinds, otherwise, there are only 8 kinds. Discuss them in categories.

If two people randomly draw lots from the branch of 10, the first step is 10. The second step, the first step is nine possibilities regardless of the result, and multiplication is used at this time.