In how many different ways can the letters of the word OPTICAL be arranged so that the vowels always come together?
The word OPTICAL contains 7 different letters.
When the vowels OIA are always together, they can be supposed to form one letter.
Then, we have to arrange the letters PTCL [OIA].
Now, 5 letters can be arranged in 5! = 120 ways.
The vowels [OIA] can be arranged among themselves in 3! = 6 ways.
$\therefore$ Required number of ways = $\left(120 \times 6\right)$ = 720.