Zach has a two numbers that have a difference of 9 and a sum of 18 what two numbers does Zach have?

Answer 1

Two numbers: x, y.

Difference: x-y = 9 (assuming x is greater than y).

Sum: x+y = 18.

Two equations, two unknowns. Solve for x or y on either equation: x = 9 + y (from the difference formula). Plug that x into the sum formula (plugging it into the difference formula would get you 9 = 9, which doesn't help us):

x + y = 18

(9 + y) + y = 18 (no more x)

9 + 2*y = 18

Solve for y:

2*y = 18-9 = 9

y = 9/2 = 4.5.

Plug this number back into either formula:

x + y = x + 4.5 = 18

x = 18-4.5 = 13.5

So x = 13.5, y = 4.5. Test to make sure it's right:

13.5 - 4.5 = 9 (we said x was greater than y)

13.5 + 4.5 = 18

This solution is unique which means that these (13.5 and 4.5) are the only numbers that satisfy you're criteria.