Algebra help? (Probability and Statistics)?

I REALLY do not understand this. Please help!

How many different 5-digit codes are possible using a telephone keypad if the first digit cannot be 0 and no digit may be used more than once?

I know the answer is 27,216. I just don't know how to obtain that answer!

HELP! :)

Well, basically all you do in this problem is multiply. I like to put down 5 blank spaces on paper and then put the number of combinations in each space. For example, there are 10 total digits that can be used (0-9). However the first digit can not be 0, so there are 9 possible combinations (1-9). The next digit cannot be the same as the first digit, but it can be 0, so there are 9 combinations. The third digit cannot be either the first or the second digit and thus there are 8 combinations. The fourth digit has 7 combinations and the fifth has 6 combinations. so if you multiply the numbers of combinations you should hav 9 x 9 x 8 x 7 x 6 = 27,216.

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