The sum of two numbers is 42. One number is 20 more than the other. Find the numbers.

X and y being variables set for #1 and #2,

x + y = 42

x = y + 20

The second equation gives (x) a value, so you substitute its value in the first equation.

x + y = 42

(y + 20) + y = 42

2y + 20 = 42

- 20 - 20

2y = 22

__ __

2 2

y = 11

Substitute y in the second equation

x = 11 + 20

x = 31

Answer : 31 and 11