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CAT 2017 Slot 2 · Quant · Number System · hard

What is the largest integer n such that 12ⁿ divides 50! (50 factorial)?

Single correct option

What is the largest integer n such that 12ⁿ divides 50! (50 factorial)?
  1. A. 16
  2. B. 22
  3. C. 23
  4. D. 24
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Answer: (B) 22

12ⁿ = 2²ⁿ × 3ⁿ, so we need enough 2s and enough 3s in 50!.

Powers of 2 in 50!: 25 + 12 + 6 + 3 + 1 = 47 ⇒ at most ⌊47/2⌋ = 23 twelves.
Powers of 3 in 50!: 16 + 5 + 1 = 22 ⇒ at most 22 twelves.

The scarcer resource decides: n = 22.

Trap: 23 comes from checking only the 2s; 16 counts only multiples of 3 once.
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Original question written in the CAT 2017 Slot 2 pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake