On a 50-question test, a student answered 5 questions incorrectly. What percent did the student answer correctly?
A. 90%
B. 45%
C. 55%
D. 10%

Question

On a 50-question test, a student answered 5 questions incorrectly. What percent did the student answer correctly?
A. 90%
B. 45%
C. 55%
D. 10%

fortytherapper · Answer

I would set up a proportion 

$$\frac{ x }{ 100% }= \frac{ 45 }{ 50 }$$
Understand how I got that, or would you like me to explain deeper?

danysanchy97 · Answer

yes please

fortytherapper · Answer

Alright.

So you want to find what percentage he got correctly. A test is worth 100%, right. So what part of the 100% did he get correct. That's where this came from:

$$\frac{ x }{ 100 }$$

Since we put a equal sign, we must match the correct numbers with the correct percentage.
They gave you 5 incorrect answers, but you're trying to find correct answers. If there are 50 total questions and he missed 5, then:

$$50-5=45$$

There were also 50 total questions, creating this:

$$\frac{ 45 }{ 50 }$$

Now if we combine then x = 45 because both represent correctness and 100 = 50 because both represent a total 

$$\frac{ x }{ 100 }=\frac{ 45 }{ 50 }$$

danysanchy97 · Answer

oh ok i understand now. thank you

fortytherapper · Answer

You're welcome. Now you can just cross-multiply and divide and then that will find X