How many numbers are there between 100 and 1000 which have exactly one of their digits as 7?

Explanation

Numbers between` 100` and `1000=900`

1) When the units place has 7



Tens place can have any one of the digits except 7.

So, it can be filled in 9 different ways.

The hundreds place can have any one of the digits except 0 and 7. So, it can be filled in 8 different ways.

Therefore, there are `9 xx 8 = 72` such numbers.


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