Twice 36 is 72, half of 36 is 18 and a quarter is 9. That’s 99, and the man makes it 100.
A man walking down the street meets a group of people and says, “If there were twice as many of you, plus half as many again as you are, plus a quarter as many, then with me there would be a hundred of us.” How many are in the group?
Give me a hintThe hint
Leave him out and the rest come to 99.
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36
Source: Alcuin of York (attributed), Propositiones ad Acuendos Juvenes, no. 2, c. 800