There are 9000 4 digit numbers
Find 4 digit numbers that are all different from 1
find 4 digit numbers that are all different from 1
The thousands digit has 8 ways to choose, hundreds, tens, and units all have 9 ways
=> there are 8 x 9 x 9 x 9 = 5832 digits
=> 4 digit numbers contain at least 1 digit 1 = number of 4 digit numbers , the number of 4 digit numbers is different by digit 1
=9000 - 5832 = 3168 numbers
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