& ltB& gt； 1. Each ball can be put into 1, 2, 3 boxes. * * There are four balls, so it is the fourth power of 3.

2. If it is five balls, it is three to the fifth power.

The balls are all the same, so no matter how they are arranged and combined, the only difference is the position.

4. There are three choices for a ball. Boxes are equivalent to different positions, and events between balls are independent of each other, so the multiplication principle of three to the fourth power is the same for five balls. The formula is: f (r, n) = c (r, n+r-1) = (n+r-1)/r (n-65538)

The people in front are so rude! ! ! ! ! ! ! ! ! ^_^