Question

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

Answer 1

First place can be filled up in $5$ ways.

After place ,we are left with $4$ flags.

$\therefore$ The second place can be filled up in $4$ ways.

The total number of signals which can be generated $=5\times 4=20$