Question

What is the solution to this system of equations?

5x-y=40
y=2x-4

A) 20, 12
B) -20, 12
C) 12, -20
D) 12, 20

Answer 1

Answer is D

{ solve simultaneously }
rearrange equation to make y the subject
5x-y=40
y=5x-40

Sub y=5x-40 into the second equation given ( y=2x-4 )

5x-40 = 2x-4

Solve normally to find x
x = 12

Sub x=12 into y=5x-40
Solve normally to find y
y = 20

Therefore, answer is D) 12, 20

Answer 2

We know what y is given the second equation, so let’s plug it in

5x - (2x - 4) = 40

Solve for x

5x - 2x + 4 = 40

3x = 36

x = 12

Plug in x for either equation

y = 2(12) - 4

y = 24 - 4

y = 20

X = 12 and Y = 20, so D