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?
10
12
20
24
36
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The three flags can be arranged in 3 ! ways to make a unique combination. Hence 4 * 3! = 24 ways.
so A has 4 cases
B has 3 cases
C has 2 cases
so there are 4x3x2=24