Question

The problem below has been solved incorrectly. Identify and explain the error.

This is the question.
Solve the following system using the method of your choice.
y=x+3
4x+y=18

The incorrect problem is attached above.
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Answer 1

If you look over the steps you can see that until 4x + x + 3 = 18, evertything is dandy. But the step after that 4x + x =21 seems a bit fishy.

Think about it they subtract 3 from both sides so the first side is correct

4x + x, but they added 3 to the other side:

`(4x+x+3) - 3 = 18 - 3\\4x+x = 15`

not

4x+x = 21

Then we solve for 4x + x = 15

`5x = 15\\x = (15)/(5) \\x = 3`

To solve for y we use :

y = x+3

y = 3+3 = 6

so (3,6) is the right answer