Question #508b6

1 Answer
May 6, 2016

a) 24 different arrangements, 4! = 24
b) 12 arrangements start with a vowel.


a) In choosing the first letter, there are 4 options, but once one has been chosen, there are only 3 tiles remaining to choose from for the second letter. Similarly there is a choice of 2 letters for the third letter, but only one letter is left for the last position.

The total number of different arrangements is therefore:
4 x 3 x 2 x 1 = 24.

This is also called 4 factorial, denoted by 4!

b) The same approach can be used if the first letter is to be a vowel.
2 of the letters are vowels, A and E.

Therefore there is a choice of 2 letters for the first position, 3 for the second, 2 for the third and no choice for the fourth place.

The number of arrangements starting with a vowel is given by:
2x3x2x1 = 12.

One could also realise that as half of the letters available are vowels, half of the total number of arrangements would start with a vowel.