# Define the variable and equation for the situation.

Walmart has a bike on sale for 150. The sign next to it says that the price is \$25 off the original price. What is the original price? Define the variable and equation for the situation. Solve the equation.

This question is from my son's Math test. His answer is as follows:

Let x = original price $$x = 150 + 25$$; $$x = 175$$.

His teacher marked it as wrong and rewrote the equation as $$x - 25 = 150$$ ; $$x= 175$$.

I don't see how the equation my son wrote is wrong? Could you please help me understand?

• The two are equivalent. Your teacher is discouraging thought in favor of process and pedantry. – John Douma Jan 23 '19 at 1:07

It is a minor detail: Let $$x$$ be the price, as above. Then it is known that $$\ 25$$ is taken off, and the price is now $$150$$. So it must be that $$x - 25 = 150$$, and consequently, $$x = 175$$.
The distinction is that your son has jumped a step in the reasoning. You do know at the very beginning of the problem that $$x = 25 + 150$$, you only know that $$x - 25 = 150$$.