An office building has elevator buttons numbered from 1 to 50. Due to a software glitch, the elevator computer completely ignores any floor number that contains the digit '4' or is a multiple of 4. How many total floors can the elevator actually visit?
27 floors
Out of 50 floors: multiples of 4 are 12 numbers (4, 8, 12... 48). Floors containing '4' are: 4, 14, 24, 34, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 (14 numbers). Overlap (multiples of 4 that also contain 4): 4, 24, 44, 48 (4 numbers). Total invalid = 12 + 14 - 4 = 22. Valid floors = 50 - 22 = 28. Wait, let's verify: 50 - 22 = 28 floors.
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: Hard. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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