Question

Mikayla and Jesse both solved the equation x−15=12−8
, using substitution. Mikayla says the answer is x=19
, and Jesse says the answer is x=27
. Which student is correct, and how do you know? Show your work and explain your thinking.

Answer 1

Mikayla is correct.

Work:
x − 15 = 12 − 8
Simplify the right side: 12 − 8 = 4, so
x − 15 = 4
Add 15 to both sides: x = 4 + 15 = 19.

Check:
For x = 19: 19 − 15 = 4 and 12 − 8 = 4, so the equation holds.
For x = 27: 27 − 15 = 12, which is not equal to 4, so 27 is wrong.

Likely mistake: Jesse may have added 12 and 15 (getting 27) instead of simplifying 12 − 8 first.