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Question
How many numbers are there between 99 and 1000 having atleast one of their digits 7?
Solution
Total number of 3 digit numbers having atleast one of their digits as 7 = (Total numbers of three-digit numbers) – (Total number of 3 digit numbers in which 7 does not appear at all).
= (9 × 10 × 10) – (8 × 9 × 9)
= 900 – 648
= 252.
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