Stacy is trying to solve the equation 2x - 5 = 10x + 7. Her first step results in the equation 2x = 15x + 12. Describe her mistake, then solve the equation correctly.

Mistake: you can't add 5 to 10x.

solution: - 1.5

Her mistake was that she tried adding like terms, but did not do it properly. She tried to remove the - 5 by adding 5 to both sides. If you started with that, the equation would look like: 2x=10x+12. As you can tell, she wasn't suppose to add any x's, since 5 is not an x.

Let's solve:

2x-5=10x+7 2x=10x+12 - 8x=12 12:-8 = - 1.5 = x

We got - 1.5 for x, let's check to make sure it's right.

2 (-1.5) - 5=10 (-1.5) + 7 - 3-5=-15+7 - 8=-8

So, X=-1.5.