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3 years ago

14

How many 7 digit phone numbers are there assuming the first digit can't be a 0 or a 1?

1 answer:

Anettt [7]3 years ago

7 0

The first digit can be any one of the numbers 2-9 That a total of 8 numbers.

The next 6 digits can be any permutation of 6 from the numbers 0 to 9.
(10 numbers)

nPr = n! / r!

so here we have 10P6 = 10! / 6! = 10*9*8*7 = 5040

So final answer is 8 * 5040 = 40,320

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