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How many 4 digit number are there with no digit repeated? Please also explain why do we need to use multiplication principle. And what is multiplication principle?

How many 4 digit number are there with no digit repeated? Please also explain why do we need to use multiplication principle. And what is multiplication principle?

Grade:11

1 Answers

Arun
25750 Points
6 years ago
we know in a 4 digits number, thousand digit can’t be zero
 
hence, for a thousndth place only 9 digits are allowed to be filled.
hence, for a hundredth place only 9 digits (including zero & besides that digit that is already filled) are allowed to be filled
hence, for a tenth place only 8 digits are allowed to be filled
hence, for a unit place only 7 digits are allowed to be filled.
 
thus total ways  = 9 * 9* 8 *7 = 4536 ways
 

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