Mathematics
How many times does the digit 3 occur at ten's place in natural numbers from 100 to 1000?
Number System
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Answer
We need to count natural numbers from 100 to 1000 in which the digit at the ten's place is 3.
Such numbers are of the form 3 (a 3-digit number with 3 at the ten's place), as the number 1000 has 0 at its ten's place.
For the hundred's place, the digit can be any of 1, 2, 3, 4, 5, 6, 7, 8 or 9 (9 choices).
For the ten's place, the digit is fixed as 3 (1 choice).
For the unit's place, the digit can be any of 0, 1, 2, 3, 4, 5, 6, 7, 8 or 9 (10 choices).
Total such numbers = 9 × 1 × 10
= 90
Hence, the digit 3 occurs at the ten's place 90 times in natural numbers from 100 to 1000.
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