sum of numbers

Question

The sum of two numbers is 21. First is 2/5 of the second number, what are the numbers?

Answer 1

The sum of two numbers (x + y) is 21:

 

x + y = 21

 

The first number (x) is 2/5 of the second number (y):

 

x = (2/5)y

 

Substitute (2/5)y in place of x:

 

(2/5)y + y = 21

 

(7/5)y = 21

 

Solve for y.  Once you have y, x = (2/5)y.  Check your answer by adding x and y to be sure they add up to 21.