52.Counting the Digit 9 up to 1000
★★★combinatoricsCh. 1 — Classical Probability and Combinatorics444+ Problems in Probability
How many times does the digit 9 occur when counting from 1 to 1000? Note that the number 919, for example, counts as two 9s.
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Count position by position: how often is the units digit a 9? The tens digit? The hundreds digit?
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