7th Grade math. Step by Step

Question

A student answers 90% of the questions on a math exam correctly. If she answers 27 questions correctly, how many questions are on the exam?

Answer 1

We know she answered 27 questions and that represents 90% of the exam.

Let x be the overall number of questions on the exam.

Then 90% of x is 27 questions.

But 90% = 90/100 = 0.9

Therefore 0.9x = 27.

Soloving for x, we have x = 27/0.9 = 30.

There are 30 questions on the exam.

 

Check your answer (always):

90% of 30 is 0.9*30 = 27. 

Answer 2

x=# of questions on the exam

90%=90/100=9/10

9/10=27/x

3*9=27

3*10=30 questions are on the exam, or...

cross multiply

9*x=10*27

9x=270

x=270/9

x=30 questions again