Question

Anne solved 5(2x−3)=20x+15 for x by first multiplying 5 and 2x on the left side of the equation. She got the answer x = −95. When she substituted −9/5 into the original equation her answer was incorrect. Explain Anne’s error, and find the correct answer.

Answer 1

Answer: x=-3

Explanation:

Anne's error is that she only multiplies 5 and 2x on the left side, she needs to multiply 5 and 2x, and also that she needs to multiply 5 and -3.

5(2x−3)=20x+15

5(2x) + 5(-3) = 20x + 15

10x - 15 = 20x + 15

-10x - 15 = 15

-10x = 30

x = -3