How many 4-digit personal identification numbers are possible if the number cannot contain a zero?

Question

Giana Mclean

Mathematics

7 January, 04:46

How many 4-digit personal identification numbers are possible if the number cannot contain a zero?

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Answers (1)

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Tomas Montgomery · Answer 1

It is given that we cannot include zero in the 4 digit PIN. So, we have only nine numbers with us, namely, 1,2,3,4,5,6,7,8 and 9.

Now, there are two possible cases for this question.

Case 1: If a digit can be used only once. i. e digits can not be repeated.

Then, the number of cases are 9*8*7*6 = 3024 possible PIN numbers.

Case 2: If a digit can be used again. i. e digits can be repeated.

Then, the number of cases are 9*9*9*9 = 6561 possible PIN numbers.