Question

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

Answer 1

No. of ways to select $2$ flags from $5$ flags${=}^5{C}_2$

Total no. of ways${}^5{C}_2\times 2!$

$=\frac{5!}{2!\times 3!}\times 2!=20$ ways