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In a certain summer school program, there are five periods in the day.

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In a certain summer school program, there are five periods in the day.

by BTGModeratorVI » Sun Jul 26, 2020 6:37 am
In a certain summer school program, there are five periods in the day. Each student takes English, Math, History, Science, and Science Lab. In how many orders can a student schedule be arranged given that Science lab must immediately follow the Science class?

A. 20
B. 24
C. 100
D. 120
E. 135

Answer: B
Source: Magoosh
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Re: In a certain summer school program, there are five periods in the day.

by Brent@GMATPrepNow » Sun Jul 26, 2020 1:08 pm
BTGModeratorVI wrote: ↑
Sun Jul 26, 2020 6:37 am
 In a certain summer school program, there are five periods in the day. Each student takes English, Math, History, Science, and Science Lab. In how many orders can a student schedule be arranged given that Science lab must immediately follow the Science class?

A. 20
B. 24
C. 100
D. 120
E. 135

Answer: B
Source: Magoosh
Take the Science, and Science Lab classes and "glue" them together to get the super class "Science-Science-Lab"
This ensures that Science Lab immediately follows the Science class

So, we now have only 4 classes: English, Math, History and Science-Science-Lab
We can arrange n objects in n! ways.
So, we can arrange these 4 classes in 4! ways (i.e. 24 ways)

Answer: B

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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