How many arrangements can be formed of the letters EXAMINATION so that vowels occupy odd places.
Look at an arbitrary arrangement with vowels in the odd
positions, say, this one:
AMANENITIXO
is composed of the two arrangements
A A E I I O
and
M N N T X
The number of distinguishable arrangements of A A E I I O is
We have to divide by the factorial of each number of indistinguishable
letters. We divided by 2! because of the 2 A's and again by 2! because of
the 2 I's.
For each of those, the number of distinguishable arrangements of M N N T X is
We have to divide by the factorial of the number of
indistinguishable letters N. So we divided by 2! because of the 2 N's.
So the total number is
× = 10800
Edwin