Let A be the set of 4-digit numbers a_1a_2a_3a_4 where a_1 > a_2 > a_3 > a_4 then n(A) is equal to

JEE Advanced Mathematics question

Let be the set of 4-digit numbers where then is equal to

Answer: (C)

Choose any 4 different digits from . They can be written in strictly decreasing order in exactly one way,

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Question ID VK-108160