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Each signal that a certain ship can make is comprised of 3 different flags hanging vertically in a particular order. How many unique signals can be made by using 4 different flags?
Option D is the correct answer.
A signal can be made using 3 flags.
We have total of 4 , so 3 can be chosen out of 4 in 4C3 = 4C1 = 4 ways
The three flags can be arranged in 3 ! ways to make a unique combination.
Hence 4 * 3! = 24 ways.