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Question
How many three-digit numbers are there?
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Solution
Available digits for filling any place = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}
Since the thousand's place cannot be zero, available digits to fill the thousand's place = 9
Number of ways of filling the ten's digit = 10
Similarly, number of ways of filling the unit's digit = 10
∴ Total number of three digit numbers = 9\[\times\]10\[\times\]10 = 900
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