Question

Account numbers for Northern Oil Company consist of five digits, If the first digit cannot be a 0, how many account numbers are possible?

Answer 1

different digits are 0,1,2,3,4,5,6,7,8,9 ( so 10 allogether )

but zero cannot be the first one

so we have 9 ways to fill the first digit, and 10ways to fill the other 4 digits

so answer = 9 x 10 x 10 x 10 x 10 ways