Question

The sum of two numbers is 88. If four times the smaller number is subtracted from the larger number, the result is 13. Find the two numbers.

Answer 1

73 and 15

Explanation:

I made two variables for this:

x = larger number

y = smaller number

Write an equation for "the sum of two number is 88" and you get:

x + y = 88

Write an equation for "four times the smaller number is subtracted from the larger number" and you get:

x - 4y = 13

I do not want an equation with both x and y in it, so I will rewrite the first one and use substitution in the second one:

x + y = 88 -- move the x to the other side

y = 88 - x

x - 4y = 13 -- substitute for y

x - 4(88 - x) = 13 -- multiply by 4

x - 352 + 4x = 13 -- move -352 to the other side, combine x's

5x = 365 -- divide by 5

x = 73

Now that I know x is 73, I go back to my first equation (x + y = 88) and I get:

73 + y = 88 -- subtract 73 from both sides

y = 88 - 73

y = 15