Each of the letters in the word STUDENT is arranged in alphabetical order. How many letters are there in the English alphabetical series between the letter that is second from the left and the one that is fourth from the right in the new letter-cluster formed?

Correct — B.
Rule: sort the letters, find both positions, count the letters strictly between them.

STUDENT sorted: D E N S T T U, both Ts kept.
Second from the left: E(5).
Fourth from the right: U, T, T, S(19).

Letters between E and S: F to R.
19 − 5 − 1 = 13 → option (b)

Why the others are wrong

• (a)
  17 — 17 would need the two letters 18 places apart. E(5) and S(19) are only 14 apart, so 13 letters lie between them.
• (c)
  11 — 11 would need the two letters 12 places apart. E and S are 14 apart, which leaves the thirteen letters F to R between them.
• (d)
  15 — 15 counts E and S themselves: 19 − 5 + 1 = 15, but 'between' excludes both ends. Skipping the sort also gives 15, from T and D in STUDENT.

These items have three steps, and each hides a slip. First sort every letter, repeats included, so STUDENT keeps both Ts. Second, count each position from its own end. Third, count the letters strictly between: the difference in positions, minus one.

In a seven-letter cluster the fourth from the right is also the fourth from the left, the middle letter. Here that is S.

Key facts

• Sorted, STUDENT reads D E N S T T U.
• E is the 5th letter of the alphabet and S the 19th.
• The letters strictly between positions p and q number q − p − 1.
• In a seven-letter cluster, fourth from the right is fourth from the left.

Common traps

• Counting E and S themselves and answering 15
• Dropping the repeated T before counting from the right
• Answering from the unsorted word STUDENT

No directly related past PYQ was found.