How many '7' in a range from '1' to '100'
By Michael Henderson •
This question appears on my daughter's Mathematics class in secondary school:
"There are 100 rooms in a hotel. Joe must number the rooms from 1 to 100 with plastic digits. How many times does he need the digit 7?"
My answer is: 07 17 27 37 47 57 67 77 87 97
Number 7 will appear 11 times. However, the book's answer on the back is: 20 times Can you explain why??
$\endgroup$ 42 Answers
$\begingroup$07,17,27,37,47,57,67,70,71,72,73,74,75,76,77,77,78,79,87,97
$\endgroup$ $\begingroup$7,17,27,37,47,57,67,70,71,72,73,74,75,76,77,78,79,87,97 So the answer is 20
(previous answer said 19, probably omitting the two 7s that are present in '77')
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