Trevor solved the system of equations below. What mistake did he make in his work?

2x + y = 5
x − 2y = 10

y = 5 − 2x
x − 2(5 − 2x) = 10
x − 10 + 4x = 10
5x − 10 = 10
5x = 0
x = 0

2(0) + y = 5
y = 5

He should have substituted 5 + 2x

He combined like terms incorrectly, it should have been 4x instead of 5x

He subtracted 10 from the right side instead of adding 10 to the right side

He made no mistake

Question

Trevor solved the system of equations below. What mistake did he make in his work?

2x + y = 5
x − 2y = 10

y = 5 − 2x
x − 2(5 − 2x) = 10
x − 10 + 4x = 10
5x − 10 = 10
5x = 0
x = 0

2(0) + y = 5
y = 5 

 He should have substituted 5 + 2x 

 He combined like terms incorrectly, it should have been 4x instead of 5x 

 He subtracted 10 from the right side instead of adding 10 to the right side 

 He made no mistake

anonymous · Answer

He made no mistakes. Follow through his work and do it yourself and you will find that those answer are correct. You could also plug the values in for x and y and see if they check out.

anonymous · Answer

ok thank you

phi · Answer

5x − 10 = 10
5x = 0

Do you see anything wrong with this step?  I do.

anonymous · Answer

ok

anonymous · Answer

i do see that i didnt see that before

phi · Answer

what happens if you add +10 to both sides?  Like this:
5x − 10 +10 = 10+10

anonymous · Answer

Sorry, he is right. I should have been wearing my glasses.

phi · Answer

do you see that -10 +10  is 0 ?
5x − 10 +10 = 10+10  becomes
5x = 10+10

phi · Answer

and 10+10 is 20  so you get
5x=20
which does not match what Tevor did in the problem

anonymous · Answer

srrry was afk so its C?

anonymous · Answer

yes

anonymous · Answer

ok thank you guys