How many numbers are there between 100 and 1000 such that at least one of their digits is 6?

numbers between 100 and 1000 = 900
Numbers between 100 and 1000 which do not have digit 6 in any place,
= 8 × 9 × 9
= 648
Unit digit could take any value of the 9 values (0 to 9, except 6)
Tens Digit could take any value of the 9 values (0 to 9, except 6)
Hundreds digit could take any value of the 8 values (1 to 9, except 6)
numbers between 100 and 1000 which have at least one digit as 6,
= 900 - 648
= 252