1.  How many numbers are there between 100 and 1000 such that at least one of their digits is 6?
A. 648
B. 252
C. 258
D. 654

Answer: Option B

Explanation:

Numbers between 100 and 1000 = 900

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 do not have digit 6 in any place = 9 × 8 × 8 = 648

 Numbers between 100 and 1000 which have at least one digit as 6

= (900 - 648) = 252