Question

Given 5 flags of different colours, how many different signals can be generated if each signal requires the use of 2 flags, one below the other?

Answer 1

Here, the upper place of the flag can be filled in 5 ways by using the 5 flags of different colours. Now the lower place of the flag can be filled in 4 ways by using the remaining 4 flags of different colours.

$\therefore$ Total numbers of signals = $4\times 5=20.$