Account numbers for Century Oil Company consist of seven digits.....?

Question

If the first digit cannot be a 0, how many account numbers are possible?

A - 80,000,000
B - 9,000,000
C - 8,000,000
D - 1,000,000

Please explain your answer or explain to me how to start this problem. Thank You.

Answer 1

9*10^6, or 9,000,000. this is so because the first digit can be 1-9, which is 9 numbers. the second, third, through seventh digit can be 0-9, or 10 choices. multiply together because these are independent events(first number does not dictate what subsequent numbers will be) to get the answer.

Answer 2

The answer is B, because you have 10,000,000 combinations in a seven digit number assuming you can use all the numerals from 0 to 9. Since 0 cannot be the first digit, subtract 1 M from 10 M and you'll get 9,000,000.