Age and system of linear equations

by MARIA
(SALT LAKE CITY, UT)

Alvin's age is three times Elga's age. The sum of their ages is " 40 ". What is Elga's age?

Let x be Alvin's age

Let y be Elga's age

x + y = 40

x = 3y

Replace x = 3y into x + y = 40

We get 3y + y = 40

4y = 40

4y/4 = 40 / 4

y = 10

So Elga is 10 years old

Alvin's age is x = 3y = 3 times 10 = 30