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?

Answer 1

Step $1:$
Finding Number of ways.
Given $4$ Flags of different colours. So,
Number of ways to fill upper vacant place$=4$
Number of ways to fill lower vacant place $=3$


Step $2:$
Using multiplication principle.
$\therefore$ Required number of signals $=4\times 3=12$
Hence, required number of signals are $12.$