Khachaturyan M.A.

For breakfast, a group of 5 elephants and 7 hippos ate 11 round and 20 cubic watermelons, while a group of 8 elephants and 4 hippos ate 20 round and 8 cubic watermelons. All elephants ate the same whole number of watermelons. And all hippos ate the same number of watermelons. However, one type of animal eats both round and cubic watermelons, while the other type is picky and eats watermelons of only one shape. Determine which type of animal (elephants or hippos) is picky and which shape of watermelon it prefers.
Let's first find out how many watermelons each animal eats for breakfast. According to the conditions, 5 elephants and 7 hippos eat 31 watermelons, while 8 elephants and 4 hippos eat 28 watermelons. We see that if we replace three hippos with three elephants, we need three fewer watermelons. Therefore, 12 elephants would eat $31-7=24$ watermelons (i.e., each one eats 2), and 12 hippos would eat $31+5=36$ watermelons (i.e., each one eats 3).

In the first group, the hippos ate 7 with $3=21$ watermelons. There were no watermelons of that shape, so hippos eat watermelons of any shape, while the elephants are picky. In the second group, the elephants ate 8 with $2=16$ watermelons. There were no 16 cubic watermelons, so elephants prefer round watermelons.

## Answer

Elephants eat only round watermelons.

## Problem