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Part ACSIR NET December 2024both-digits-must-be-selected-first

Both digits must be selected first

How many 4-digit numbers can be generated from the digits 1, 2, 3, 4, 5 such that no digit appears more than once, and digit 1 is always somewhere to the left of the digit 2?

  1. A.72
  2. B.36✓
  3. C.12
  4. D.6

You have the answer. Trap Analysis is why the other three were written.

Not a worked solution repeated four times — the specific reasoning error each wrong option was built to reward.

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