Re: How many times will the digit 7 be written when listing the
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27 Dec 2019, 04:17
You can count numbers separately that their unit digit, tens digit and hundreds digit are equal to 7.
First, numbers that their units digit is 7: 7, 17, 27, ... ,997. There are 100 numbers [(997-7)/10+1].
Second, numbers that their tens digit is 7: 70,71, ..., 79 - 170,171,...,179 - ... - 970,971,...,979. There are 100 (10*10) numbers.
Third, numbers that their hundreds digit is 7: 700, 701, ..., 799. There are 100 numbers [(799-700)+1].
In total, the digit 7 will be written 300 times when listing the integers from 1 to 1000.