Question

11. A 7-digit phone number may not have a 1, 0, or 7 as the first digit but i thenthe rest of the number may use repetition of digits. How many possible phone numbers are there? formula: nCr= n! /(nr)!r!)

Answer 1

Ariel, this is the solution:

Possible phone numbers =

7 * 10 * 10 * 10 * 10 * 10 * 10

Possible phone numbers =

7,000,000 (7 Million)