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

Since there are 7 flags of different colours, therefore, first flag can be selected in 7 ways. Now, the second flag can be selected from any one of the remaining flags in 6 ways. Hence, by the fundamental principle of multiplication, the number of flag is 7 $\times$ 6 = 42.