Question

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

Answer 1

Use of permutation so according to problem how to arrange 7 objects taken 2 at a time 

so as there are only two flags be arranged with 7 different colors so the first flag can be arranged in any 7 ways and as for the second flag we have only 6 flag left(as 1 flag is already used) so it can be arranged in 6 ways

 so 7 × 6 = 42 ways it can be arranged