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JEE Main 2017 · Mathematics · Permutations and Combinations · hard

How many 5-digit numbers divisible by 4 can be formed using the digits 0,1,2,3,4,5 without repetition?

Single correct option

How many 55-digit numbers divisible by 44 can be formed using the digits 0,1,2,3,4,50,1,2,3,4,5 without repetition?
  1. A. 120120
  2. B. 144144
  3. C. 156156
  4. D. 168168
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Answer: (B) 144144

A number is divisible by 44 if its last two digits are. Using distinct digits from 00--55, the valid endings are 04,12,20,24,32,40,5204,12,20,24,32,40,52. For endings containing 00 (04,20,4004,20,40), the remaining 44 digits are all non-zero, so the first three places can be filled in 4⋅3⋅2=244\cdot3\cdot2=24 ways each: 7272. For endings without 00 (12,24,32,5212,24,32,52), the leftover digits include 00, which cannot lead: 3⋅3⋅2=183\cdot3\cdot2=18 ways each: 7272. Total =144=144.
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