A book has pages numbered from 1 to 100. How many total pages contain the digit '7' at least once?
19
Count the pages with a 7 in the units place (7, 17, 27, 37, 47, 57, 67, 77, 87, 97 -> 10 pages) and the tens place (70, 71, 72, 73, 74, 75, 76, 77, 78, 79 -> 10 pages). Page 77 is counted in both lists, so subtract 1. Total: 10 + 10 - 1 = 19 pages.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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