Question

A student got an 85% on his test . If he got 12 questions wrong , how many questions were on the test?

Answer 1

80 questions

Explanation:

Given that a student received an 85% grade on his test, and that he got 12 questions wrong:

We could infer that if he answered all of the test questions correctly, then he would have received a perfect score of 100% on his test.

Since he got 12 questions wrong, then it means that those wrong answers account for the 15% out of receiving a 100% grade on his test (or: 100% - 85% = 15%).

Let x = number of test questions

In order to find how many questions were on his test:

12 questions = 15% (or 0.15) of the total number of questions (x)

12 questions = 0.15x

Divide both sides by 0.15 to isolate x:

`\displaystyle\mathsf{(12\:questions)/(0.15)\:=\:(0.15x)/(0.15)}`

x = 80 questions

Therefore, there were 80 questions on his test.