There are 10 boys and 7 girls.
A boy and a girl have to be chosen for the school board.
How many possible pairs can be chosen from 10 boys and 7 girls?
For the 1st boy, any one of the 7 girls can be chosen, so 1×7 = 7 pairs
For the 2nd boy, any one of the 7 girls can be chosen, so 1×7 = 7 pairs
For the 3rd boy, any one of the 7 girls can be chosen, so 1×7 = 7 pairs
As you can see the pattern, for each boy there are 7 choices of girls so we can write
10×7 = 70 pairs
Therefore, 70 possible pairs can be chosen from 10 boys and 7 girls.