a phone company wants to create some new area codes. each area code will be 3 numbers . using the digits 1,5,and 7 only once in each code, how many codes can the phone company create?

Answer 1

There are 3 ways to choose the first digit.

Then, there are only 2 ways to choose the second digit.

Then, the left-over digit will be third.

So, there are 3*2*1 = 6 different area codes:

157
175
517
571
715
751