Question

A first number plus twice a second number is 3. Twice the first number plus the second totals 21 . Find the numbers.

Answer 1

x = 13

y = -5

Explanation:

Let x = the first number

Let y = the second number

x + 2y = 3 2x + y = 21

You have two unknowns, so you need to equations to solve.

Solve the first equation for x:

x + 2y = 3

x = -2y + 3 Substitute this in for x in the second equation.

2x + y = 21

2(-2y + 3) + y = 21 Distribute the 2

-4y + 6 +y = 21 combine the y's

-3y = 15 Divide both sides by -3

y = -5

Plug -5 back in for either equation

x + 2y = 3

x + 2(-5) = 3

x -10 =3

x = 13