When to use arrangement and when to use combination depends on the specific topic. Some questions can be arranged or combined.
2. The probability that the I-th person draws the white ball is: P=A/(A+B). This is exactly the same as the probability of drawing first or drawing later. It is difficult to draw, so the lottery is fair. This conclusion can be proved by the formula of total probability. Take two people as an example: m and n stand for 1, 2 two people touch the white ball, and * stands for the opposite event.
P(M)=A/(A+B)
P(N)=P(M)P(N|M)+P(M*)P(N|M*)
= A/(A+B)*(A- 1)/(A+B- 1)+B/(A+B)* A/(A+B- 1)
=A/(A+B)