(1) The sum of the prices of a basketball and a volleyball is: 42+28=70 yuan.

∴2 10÷70=3

Explain that you should buy three basketballs and three volleyball.

(2) If you buy a basketball, the remaining 2 10-42= 168 (yuan).

The quantity of volleyball to be purchased is: 168÷28=6 (pieces).

Then the total is 1+6=7 (pieces).

. . . . . .

So, everyone buys three.