1: There are 90 ping-pong balls in the sporting goods. If every two are packed in a box, can they be packed properly? If you pack a box every five, can you finish it? Why?

90#2=45 boxes

90#5= 18 boxes

Answer: If one is packed in every two cases, it can be packed completely. If it is packed in five boxes, it can also be packed accurately. Because 90 is divisible by 5.

There are 57 balls in the sporting goods store, and every three balls are packed in a box. Can they be properly packed?

57#3+ 19 cases

Answer: I can just finish it.