Question

Given $4$ flags of different colours, how many different signals can be generated, if a signal requires the use of $2$ flags one below the other?

• A. $12$
• B. $13$
• C. $14$
• D. $15$

Answer 1

Answer: (A)

$12$

Answer 2

There will be as many signals as there are ways j of filling in $2$ vacant places $\boxminus$, in succession by the $4$ flags of different colours. Hence, by the multiplication j principle, the required number of signals $= 4 \times 3 = 12$.