by David, 30 September 2020 | 0 comments

Difficulty: Taxing Grab a calculator (or a pen and paper) Choose a three-digit number (e.g. 123) Multiply it by 7 Multiply the answer by 11 Multiply that answer by 13 You will get your starting number written out twice! (e.g. 123 123) The question is, can you work out why?

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by David, 16 September 2020 | 1 comments

Difficulty: Tricky We’re going to make a magic triangle! Take the numbers 1–6 and arrange them in a triangle with three numbers on each side. Swap them around until the sides all add up to the same number.

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by David, 26 August 2020 | 1 comments

Difficulty: Taxing Here’s a beautiful artwork from 1895, titled Mental calculation. In public school of S. A. Rachinsky, painted by Nikolay Bogdanov-Belsky. Can you solve the puzzle the kids are pondering? If you can’t quite see the equation, here it is:

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by David, 19 August 2020 | 0 comments

Difficulty: Tricky Gertrude has a collection of shapes that she likes to arrange in patterns. She starts with a regular hexagon with 10 cm sides, and three regular triangles that also have 10 cm sides. She arranges the triangles around the hexagon, and then lines them up. In the end, one side of each triangle…

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by David, 3 August 2020 | 4 comments

Difficulty: Fun I’m thinking of three numbers. They are consecutive counting numbers. When you add the first two numbers together, you get the third number. What numbers am I thinking of?

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by David, 22 July 2020 | 1 comments

Difficulty: Tricky Ari was 10 on her last birthday, and will be 12 on her next birthday. How can this be true? Lachlan was 8 on his last birthday, and will be 12 on his next birthday. How can this be true?

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by David, 8 July 2020 | 4 comments

Difficulty: Taxing Terri’s destructive testing lab is very popular. The most important piece of equipment is an electric-powered ram that smashes into samples to see how tough they are. It’s powered by capacitors, and by changing the number of capacitors that are plugged in, Terri can control how powerful the ram is.

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by David, 24 June 2020 | 3 comments

Difficulty: Fun The extension is finished! Five new classrooms have been added to the main building. But there’s a problem. The corridor to the new classrooms is very busy. When the bell goes, lots of students stream out of the extension, while others rush in. It gets really crowded!

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by David, 10 June 2020 | 4 comments

Difficulty: Tricky Dolly bought a special cheese. It comes in a square block that’s 5 centimetres wide, 5 centimetres deep and 5 centimetres tall. It’s also coated in wax on all sides. Without removing the wax, Dolly cuts the cheese into 1 centimetre cubes. Can you work out how many cubes have wax on them?

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by David, 27 May 2020 | 2 comments

Difficulty: Fun Ash and Stacy Brull have five daughters. Each of their daughters has one brother. How many people are there in the Brull family?

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