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Suppose a designer has a palette of 11 colors to work with, and wants to design
a flag with 4 vertical stripes, all of different colors.
How many possible flags can be created?
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First vertical strip can be any of 11 colors.
Second vertical strip can be any of remaining 10 colors.
Third vertical strip can be any of remaining 9 colors.
Fourth vertical strip can be any of remaining 8 colors.
Hence, the total number of differently colored flags is the product
of four integer numbers, starting from 11, in descending order
11*10*9*8 = 7920. <<<---=== ANSWER
Solved.