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NDA 2025 Maths · Mathematics · Permutations and Combinations · medium

The number of ways in which 5 beads of different colours can be strung on a necklace is

Single correct option

The number of ways in which 5 beads of different colours can be strung on a necklace is
  1. A. 2424
  2. B. 1212
  3. C. 6060
  4. D. 120120
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Answer: (B) 1212

Circular arrangements of 5 distinct objects number 4!=244!=24. A necklace can be flipped over, so each arrangement coincides with its mirror image: 4!2=12\frac{4!}{2}=12. Stopping at 2424 is the trap.
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Original question written in the NDA 2025 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake