The sum of two numbers is 57 and the difference is 21 . What are the numbers?

Question

The sum of two numbers is 57 and the difference is 21 . What are the numbers?

Answer 1

x + y = 57 and x - y = 21

Solve for one of the variables in one of the equations:

x - y = 21 -> x = 21 + y

Substitute the "x' into the other equation and solve for 'y':

(21 + y) + y = 57 -> 21 + 2y = 57 -> 2y= 57 - 21 -> 2y = 36 -> y = 18

Now substitute this 'y' into one of the equations and solve for 'x':

x + 18 = 57 -> x = 57 - 18 -> x = 39

Check:

39 + 18 = 57 and 39 - 18 = 21

So, the two numbers are: { 39 , 18 }