BTGmoderatorLU wrote:Source: Magoosh
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
Alternate approach:
Since Science class must be followed immediately by Science lab, Science class cannot be taken during the last period.
Thus:
Number of options for Science class = 4. (Any of the first 4 periods.)
Number of options for Science lab = 1. (Must be the period immediately after Science class.)
Number of ways to arrange the remaining 3 classes = 3! = 6.
To combine the options above, we multiply:
4*1*6 = 24.
The correct answer is
B.
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