How many 7-digit phone numbers can be formed if the first digit cannot be 0 and repetition of digits is allowed?

Question

raden · Answer

the first, digit always 9 ways (1,2,3,4,5,6,7,8,9)
and the others can be chosen from anything (0,1,2,3,4,5,6,7,8,9)

mathmale · Answer

What an interesting question!
There are 10 digits, 0 through 9.
If the first digit cannot be 0, then we have 9 digits to chose from (instead of 10).
After that there are 6 more digits to choose from; each could be any digit from 0 through 9.

So, I'd venture that the number of combinations would be 8(9!).

I'd invite commentary from others on OpenStudy.

anonymous · Answer

well, here are the possible answers:

7,000,000
9,000,000
181,400
or
none of the above

raden · Answer

it is
9 * 10 * 10 * 10  10 * 10 * 10 = 9 * 10^6

anonymous · Answer

ahhh okay that sorta helps out. lemme try and figure it out.

anonymous · Answer

9000000. ty very much

raden · Answer

that's correct.

you're welcome

mathmale · Answer

Nice work, RadEn!  I should have known better.

anonymous · Answer

thanks for the help anyway mathmale!