Math Riddles

The best math riddles out there can be found on Riddles For Us.

Water balloons

Robert and David were preparing to have a water balloon fight. "No Fair" cried Robert, "You have 3 times as many as I do!" David said "Fine!" and gave Robert 10 more balloons. "Still not fair!" argued Robert, "You still have twice as many as I do." How many more balloons must David give Robert for them to have the same number?

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Melons

Farmer Brown came to town with some watermelons. He sold half of them plus half a melon, and found that he had one whole melon left. How many melons did he take to town?

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Average: 8 (1 vote)
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Lunch money

John noticed that the amount he was paying for his lunch was a rearrangement of the digits of the amount of money he had in his pocket, and that the money he had left over was yet another rearrangement of the same three digits! How much money did John start with?

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Average: 8 (1 vote)
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Seven times

What is the smallest whole number that is equal to seven times the sum of its digits?

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Two by two

You know 2 + 2 comes to the same as 2 x 2. Now find a set of three different whole numbers whose sum is equal to their total when multiplied.

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Average: 8 (1 vote)
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Knight moves

I have a calculator that can display ten digits. How many different ten-digit numbers can I type using just the 0-9 keys once each, and moving from one keypress to the next using the knight’s move in chess? (In chess, the knight move in an L-shape – one square up and two across, two squares down and one across, two squares up and one across, and other like combinations)

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Card riddle

A small number of cards has been lost from a complete pack. If I deal among four people, three cards remain. If I deal among three people, two remain and if I deal among five people, two cards remain. How many cards are there?

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The water level in a reservoir

The water level in a reservoir is low, but doubles every day. It takes 60 days to fill the reservoir. How long does it take for the reservoir to become half full?

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Average: 8 (2 votes)
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