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Difficulty: Tricky Can you take 2 from FIVE and leave 4?

Difficulty: Tricky While out adventuring, Heracles the Hero came across a monstrous, 9-headed Hydra. Without pausing to think, Heracles pulled out his sword and started cutting off the Hydra’s heads. After several minutes of cutting, Heracles realised it was taking ages to remove the heads. Then he remembered something his friend Euripides told him.

Difficulty: Fun Can you add one symbol below to make half a thousand? 5 5 5 5 5

This brainteaser comes from our new book, Puzzles and Projects. This book features some of the best puzzles, hands-on activities, stories and more from Double Helix magazine. Plus, there’s stacks of new content to explore! You can buy a copy on the CSIRO Publishing website, or pick it up from your favourite bookstore!

Difficulty: Tricky Sian is making a big, shiny cube in Minecraft. It will be 10 blocks wide, 10 blocks deep and 10 blocks high. The outer layer of blocks will be made of gold. Everything inside the cube will be made of obsidian. Will Sian need more gold blocks, or more obsidian ones?

Misrak was looking at the birthdays in her family. After a bit of maths, she realised that her father’s age and her grandfather’s age had the same digits, but swapped. When she added their ages together, she got 121. Her grandfather was aged between 20 and 40 when her father was born. Can you work […]

Difficulty: Tricky Ollie the space octopus is lost! She’s trying to get back to her home planet – the blue circle – and she needs some help. Ollie’s spaceship has special engines. They cause the spaceship to fly in a straight line, but whenever they hit a yellow star, they must make a right-angle turn. […]

Difficulty: Fun How well do you know your dice? A standard dice is a cube with six sides. Each side is numbered with a different number from 1–6. Most six-sided dice also have a special trick in the way they are numbered. If you add the number on the top and the number on the […]

Difficulty: Extreme I’m thinking of a number. When you add one and a half to it, you get the same result as if you multiplied it by one and a half. What’s the number I’m thinking of?

By Rok Willesee Difficulty: Fun An engineer has asked you to help him count the number of triangles in this roof truss. He thinks there are five, but his boss thinks there are more. How many triangles can you see?