A signal can use 2, 3, 4, or 5 flags arranged in order (one below the other) on a vertical staff, from 5 different available flags. How many different signals are possible?
A$320$
B$60$
C$20$
D$120$
Answer & Solution
Correct answer: A. $320$
2-flag: $5 \cdot 4 = 20$. 3-flag: $5 \cdot 4 \cdot 3 = 60$. 4-flag: $5 \cdot 4 \cdot 3 \cdot 2 = 120$. 5-flag: $5! = 120$. Total: $20 + 60 + 120 + 120 = 320$.
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