Q16 ARITHMETIC PROBLEMS

A string of three English letters is formed as per the following rules:

a. The first letter is any vowel

b. The second letter is m, n or p

c. If the second letter is m then the third letter is any vowel which is different from the first letter.

d. If the second letter is n then the third letter is e or u.

e. If the second letter is p then the third letter is the same as the first letter.

How many strings of letters can possibly be formed using the above rules?

First of all, make a structure of what all the possible combinations are:
With m as the middle letter -(vowel) m (another vowel)
With n as the middle letter -(vowel) n (e or u)
With p as the middle letter -(vowel) p (same vowel)
The number of possible letter strings is -
With m: 5×4=20,

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