How many words can be formed by arranging the letters of the word
How many words can be formed by arranging the letters of the word ‘ARRANGEMENT’, so that the vowels remain together?
To find: number of words where vowels are together
Vowels in the above word are: $A, A, E, E$
Consonants in the above word: R,R,N,G,M,N,T
Let us denote the all the vowels by a single letter say $Z$
$\Rightarrow$ The word now has the letters, R,R,N,G,M,N,T,Z
$\mathrm{R}$ and $\mathrm{N}$ are repeated twice
Number of permutations $=\frac{8 !}{2 ! 2 !}$
Now $Z$ is comprised of 4 letters which can be permuted amongst themselves
A and E are repeated twice
$\Rightarrow$ Number of permutations of $Z=\frac{4 !}{2 ! 2 !}$
$\Rightarrow$ Total number of permutations $=\frac{8 ! \times 4 !}{2 !^{4}}=60480$
The number of words that can be formed is 60480