5*2=?; 10:?=2; 7*3=?; ?:3=7; 3*9=?; ?:9=3

Решение:

1. 5 * 2 = 10
2. 10 : 5 = 2
3. 7 * 3 = 21
4. 21 : 3 = 7
5. 3 * 9 = 27
6. 27 : 9 = 3