Permutations & Combinations
Dictionary Order of Permutations
nta_pyq_2025_apr
Grade 11

Question:

The letters of the word KANPUR are written in all possible orders, and these words are written in dictionary (alphabetical) order. The word that appears at the $440^{\text{th}}$ position is
PRNAUK
PRKANU
PRKAUN
PRNAKU

Step-by-Step Solution

Key Concept: Fix each letter position in alphabetical order and count $5!$, $4!$, $3!$ blocks to narrow down to the exact 440th word.
Sorted letters: A, K, N, P, R, U. A…: $5!=120$ (positions 1–120). K…: $5!=120$ (positions 121–240). N…: $5!=120$ (positions 241–360). PA…: $4!=24$ (positions 361–384). PK…: $4!=24$ (positions 385–408). PN…: $4!=24$ (positions 409–432). PRA…: $3!=6$ (positions 433–438). PRKA…: remaining letters N, U in order: PRKA**N**U (439), PRKA**U**N (440). The $440^{\text{th}}$ word is **PRKAUN**.
Correct Answer: 3

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