Question

How many seven digit telephone numbers are possible the first digit cannot be three and the number must be a multiple of 10

Answer 1

900,000.

Explanation:

If the number is a multiple of 10 it must end in zero.

The first digit can be any one of 0-9 except 3 - that is one of 9 digits.

All other positions (2nd to 6th) can be any one of 0 to 9 (10 digits).

So the number of possible telephone numbers is:

9*10*10*10*10*10

= 900,000.