In a secure facility, a guard checks security logs every time someone enters or leaves. Alice enters at 8:00 AM, Bob leaves at 9:00 AM, Charlie enters at 10:00 AM, and Diana leaves at 11:00 AM. No one else enters or leaves. If the building started completely empty at midnight, how many people are inside the facility at 12:00 PM?
Two people.
Alice entered and stayed. Bob left (meaning he was already inside). Charlie entered and stayed. Diana left (meaning she was already inside). So Alice and Charlie are inside, totaling 2.
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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