Question

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

Answer 1

Given : 5 different colour flags. 

To find: Number of different signals, using 2 flags

We have to select two flags one after the other. Therefore the upper flag (first flag) can be selected in 5 ways. Since both flags must be different colour, lower flag (second flag) can be selected in 4 ways. 

∴ Number of different signals = 5 x 4 = 20