Question

How many 4 digit number can made using 1,2,3,4,5,6 and 7 with none of?

Answer 1

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This is a question on Permutations where order matters.

No of 4 digit numbers that can be formed using 1,2,3,4,5,6 & 7 where none of digits is repeated is denoted by P(7,4)

P(7,4) = 7!/3! =7 x 6 x 5 x 4 = 840

For that matter, this answer is valid for any 7 distinct digits except 0.