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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Average: 9 (2 votes)
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My twin lives at the reverse of my house number

My twin lives at the reverse of my house number. The difference between our house numbers ends in two. What are the lowest possible numbers of our house?

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Average: 9 (2 votes)
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Rope

A man ordered a length of rope by telephone from his nearest hardware shop. But when he went to collect the rope, he found that the assistant had miswritten the order by interchanging feet and inches. As a result of this, the rope was only 30 percent of the length that the man wanted. What length did he want and what length did he get?

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Average: 8 (1 vote)
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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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Average: 8 (1 vote)

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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Average: 8 (1 vote)
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