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King School has an enrollment of 900 students. The school day

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by BTGModeratorVI » Fri May 29, 2020 6:46 am

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King School has an enrollment of 900 students. The school day consists of 6 class periods during which each class is taught by one teacher. There are 30 students per class. Each teacher teaches a class during 5 of the 6 class periods and has one class period free. No students have a free class period. How many teachers does the school have?

A. 25
B. 30
C. 36
D. 60
E. 150

Answer: C
Source: Official guide
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Source: — Problem Solving |

BTGModeratorVI wrote:
Fri May 29, 2020 6:46 am
King School has an enrollment of 900 students. The school day consists of 6 class periods during which each class is taught by one teacher. There are 30 students per class. Each teacher teaches a class during 5 of the 6 class periods and has one class period free. No students have a free class period. How many teachers does the school have?

A. 25
B. 30
C. 36
D. 60
E. 150

Answer: C
Source: Official guide
There are 900 students, and there are 30 students per class.
900/30 = 30
So, at any given time during the school day, there are 30 class periods happening.

Since there are 6 class periods per day, the TOTAL number of classes each day = (6)(30) = 180

Each teacher teaches 5 classes per day
If there are 180 classes per day, then the number of teachers = 180/5 = 36

Answer: C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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My solution:

At any point in time, only 5/6 of the teachers are teaching a class, but every student is in class. Therefore we know the following:

Total Student Body / Students per Class = # of teachers currently teaching
900 / 30 = 30 teachers currently teaching

If we know that only 5/6 of teachers are every teaching at one time then the total # of teachers must be:
30/(5/6) = 30*6/5 = 36

Answer C
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