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I need to know "How" to calculate total number of combinations that are possible to generate 4 character string having a pattern of Letter-Number-Letter-Number.

The complexity are: strings should be unique, and vowels should be excluded (not to use them in calculation).

Can there be a specific formulae to find that?

Any help is appreciated.

Thanks

GDG
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1 Answers1

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I assume by "number" you mean "digit"

You can put any letter in the first position, so there are $21$ possible starts. For each such string, you can put any of the digits fom $0$ to $9$, giving you $10$ possible digits. On the third position, you can put another letter, any letter except for the one in the first place, so $20$ possibilities. Then there are $10$ possibilities at the last position.

5xum
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  • Thanks a lot, that solves my problem... so both answers are one in same - 21 * 10 * 20 * 10.... thanks once again. – GDG Mar 11 '14 at 09:26