Question

 A company places a seven-digit serial number on each part that is made. Each digit of the serial number can be any number from 0 through 9.Digits can be repeated in the serial number. How many different serial numbers are possible?

Answer 1

Since digits can be repeated and each digit can take any position in the serial number, there are 10 ways of choosing each digit. Thus,

$N=10^7=10,000,000$

10,000,000 serial numbers are possible.