Of the students at a certain high school, 90 . . .

[VJesus12]

Of the students at a certain high school, 90 percent took a course in algebra or geometry and 15 percent took courses in both. If the percent of students who took a course in algebra was 2 times the percent of students who took a course in geometry, what percent of the students took a course in algebra but not geometry?

A. 35%
B. 50%
C. 55%
D. 60%
E. 70%

The OA is C.

I am not sure about how to solve this PS uqestion. May any expert give me some help? Thanks.

[EconomistGMATTutor]

Hello Vjesus12.

Let's suppose that there are 100 students. So, we have the following equations:

A or G = 90.
A and G = 15.
A= 2G
A without G= ?

Now,

A or G = A + G - (A and G)
90 = 2G + G - 15
105 = 3G
G = 35.
A= 70.

A without G = A - (A and G) = 70 - 15 = 55.

So, the correct answer is 55%, that is to say C.

I really hope this way of explanation may help you to understand it better.

Feel free to ask me again if you have a doubt.

[Scott@TargetTestPrep]

Of the students at a certain high school, 90 percent took a course in algebra or geometry and 15 percent took courses in both. If the percent of students who took a course in algebra was 2 times the percent of students who took a course in geometry, what percent of the students took a course in algebra but not geometry?

A. 35%
B. 50%
C. 55%
D. 60%
E. 70%

The OA is C.

I am not sure about how to solve this PS uqestion. May any expert give me some help? Thanks.

Let x = the percent of students who took geometry; thus, 2x = the percent of students who took algebra. We can create the equation:

x + 2x - 15 = 90

3x = 105

x = 35

So 2(35) = 70 percent of the students took algebra, and 70 - 15 = 55 percent of the students took algebra but not geometry.

Answer: C