Question

A student solved a system of equations by elimination. The answer is not correct. Describe the error in the solution.

Original Problem:

3x−2y=8

x+y=2

Student Work:

3x−2y=8

2x+2y=2

5x=10

x=2

Answer 1

The student went from x+y = 2 to 2x+2y = 2, which is not correct. They multiplied the left side by 2, but forgot about the right hand side.

They should have gone from x+y = 2 to 2x+2y = 4 after multiplying both sides by 2.

So they should have this new equivalent system

`\begin{cases}3x-2y = 8\\2x+2y = 4\end{cases}`

Add straight down and we end up with the new equation 5x = 12 which solves to x = 12/5 = 2.4

Use that x value to solve for y. You should get y = -2/5 = -0.4