The sum of two integers is 12, and their product is 27.What are the two integers?

Well since 1, 3 and 9 are the only numbers that will divide into 27 evenly, what do you think.

If you know algebra, you'll go like this:

Let the first integer be x and other other y.

Their sum is 12, hence x + y = 12

Their product is 27, hence xy = 27

Solve the two simultaneous equations.