Question

Given 7 flags of different colours, how many different signals can be generated if a signal requires the use of two flags, one below the other?

Answer 1

Number of flags = 7
∴ Number of ways of selecting one flag = 7
Number of ways of selecting the other flag = 6 (as only 6 colours are available for use)
A signal requires use of two flags
∴ Total number of signal that can be generated = 7$\times$6 = 42