Question

How many four letter words are possible using the first 5 letters of the alphabet if the first letter can not be a and adjacent letters can not be alike?

Answer 1

The first five letters are `A,B,C,D,E`

Consider this box.

Each `1,2,3,4` places represent place of a letter.

First place `1` can be filled in `4` ways. (Excluding A)
First place `2` can be filled in `4` ways.
First place `1` can be filled in `3` ways.
First place `1` can be filled in `2` ways.
First place `1` can be filled in `1` ways.

Total number of ways`=4*4*3*2*1=96 ways`

Hence `96` letters can be made.