1. Variant 1.

Masha is distributing tennis balls into identical boxes. If she uses 4 boxes, there is still room for 8 more balls in the last box, and if she uses 3 boxes, 4 balls will not fit into the boxes. How many balls is one box designed to hold?
Answer: 12

Solution.

Method 1

Notice that if the balls are in 3 boxes, there are 4 tennis balls left. Take these 4 balls and put them in the fourth box. According to the condition, there will still be room for 8 more balls in this box. This means that the box can hold a total of 12 balls.

Method 2.

Let the box hold $x$ balls. Then $3 x+4=4 x-8$. From this, $x=12$.