What two numbers add up to make seven and multiply together to make three?

Answer 1

This is equivalent to solving the simultaneous equation set {x, y: x + y = 7, xy = 3}.

By rearranging and substituting, we find that x = 7 - y, and that (7 - y)y = 3.

We can expand and simply to gain -y2 + 7y - 3 = 0, a relatively simple equation called a quadratic, and one which has a precise formula for its solution.

Using this formula, we find that y = 0.459 and y = 6.541. Note that because these add to 7, we will end up with the same answers for x, i.e. for y = 0.459, x = 6.541 and vice versa.

Regardless of the way you choose to then label the numbers, the solution is (0.459, 6.541). These add to 7 and multiply to 3.