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If 1 2 · ( 15 C 1 ) + 2 2 · ( 15 C 2 ) + 3 2 · ( 15 C 3 ) + … + 15 2 . ( 15 C 15 ) = 2 m . 3 n . 5 k , where m, n, k   , then m + n + k is equal to :

1. 18
2. 19
3. 21
4. 20

Correct answer: 19

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