How many unique five digit codes can be made if the first di

How many unique five digit codes can be made if the first digit cannot be a zero and each digit can be used more than once?

Solution

We have 5 blanks to fill, except the first has restricted to can\'t be zero. Each blank can be filled with 10 digits ( 0,1,2,3,4,5,6,7,8,9) and the first blank be filled in 9 digits.

Number of unique 5 digit codes be = 9*10*10*10*10 = 90000