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NDA 2016 Maths · Mathematics · Permutations and Combinations · hard

The number of three-digit numbers with all digits distinct that are divisible by 5 is

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The number of three-digit numbers with all digits distinct that are divisible by 55 is
  1. A. 136136
  2. B. 144144
  3. C. 128128
  4. D. 180180
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Answer: (A) 136136

The last digit is 0 or 5. If it is 0, the first two places can be filled in 9×8=729\times8=72 ways. If it is 5, the first digit cannot be 0 or 5, giving 8 choices, and the middle digit has 8 choices (any digit except the two used, including 0), so 8×8=648\times8=64. Total 72+64=13672+64=136.
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Original question written in the NDA 2016 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