SAT Math : How to find the greatest or least number of combinations

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1891 : Psat Mathematics

There are seven unique placemats around a circular table. How many different orders of placemats are possible?

Possible Answers:

Correct answer:

Explanation:

Since the table is circular, you need to find the total number of orders and divide this number by 7.

The total number of different orders that the placemats could be set in is 7! (7 factorial).

7!/7 = 6! = 720

 

Note that had this been a linear, and not circular, arrangement there would be no need to divide by 7. But in a circular arrangement there are no "ends" so you must divide by N! by N to account for the circular arrangement.

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