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Math

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Confused on permutation or combination on this question:

A VISA credit card has a first digit of 4 followed by 15 other digits. How many different VISA accounts does this allow?

I know the formulas but I am having a hard time determining which one to use. Help!!!

  • Math -

    We have a choice of 10 digits at each of the following digits, so the total number of choices is
    10^(15).

    In real life, the last digit (16th) is used for validation purposes, and is not a free choice. There number of "free" digits is therefore limited to 14. But that's not part of the math question.

  • Math -

    Thank you!

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