Explanation:

The 5 letters can be written in 5! ways.
Then n(S) = 5!

Let E be the event that the letters y and z are written down side by side.
(i.e., y and z are always come together).
Now the alphabets v, w, x and (yz) can be written in 4! ways.
And y, z written in 2 different ways.
Then, n(E) = 4! x 2!
Therefore p(E) = 4! x 2!/5! = 2/5.

Hence, option 3 is the correct answer.