# Blog

## Massive multiplication

By David Shaw, 10 April 2024

Sienna’s teacher is writing up a wicked problem. First, the teacher writes all the numbers from 1 to 99 and then erases 10, 20, and all the other numbers that end in 0. “Listen up! Multiply all these numbers. Tell me the last digit and I’ll give you full marks on your next assignment.”

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## Brainteaser: Skipping stairs

By Ariel Marcy, 21 March 2024

Flora likes to run up stairs as fast as she can! Sometimes she lands on every stair and sometimes she skips a stair, taking two in one stride. This gets her thinking: how many different ways can she run up a staircase?

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## Secret pairs

By Ariel Marcy, 12 March 2024

Lavonne is testing a secret code with her friend Jack. First, she picks 3 different secret numbers between 1 and 9. Then she finds the sum of each pair of numbers. Lavonne wants to know if Jack can figure out the original secret numbers just from the sums?

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## Brainteaser: Egg-cellent farming

By Ariel Marcy, 26 February 2024

Farmer Wallace packages his eggs in cartons that hold a dozen eggs. In March, he sells 5 standard orders of eggs to the local grocery store. Each standard order consists of 4 grosses of eggs. A gross is 144 eggs. How many cartons of eggs did Farmer Wallace sell?

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## Brainteaser: Space climb

By Ariel Marcy, 13 February 2024

Catalina won a game show prize! She spent 3/4 of it on a trip into space. She spent 2/3 of her remaining money climbing Mount Everest. Finally, she donated the last $100,000 to wildlife. How much did she win?

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## Artful measuring

By Ariel Marcy, 10 January 2024

Holly loves drawing and her favourite colours have been sharpened a lot. Her most favourite colour, rose, is exactly 3cm long. She discovers that the teal pencil is exactly 4cm, and the almond pencil is exactly 6cm. What lengths from 1-10 cm can Holly make with her pencils?

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## 2023’s Best Brainteasers

By Ariel Marcy, 14 December 2023

In 2023, Double Helix readers busted a bunch of brainteasers! Here are the tippy-top, most popular puzzles of the year.

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## Same, same, same but different

By Ariel Marcy, 6 December 2023

Can you find a different set of 5 positive whole numbers with the same stats?

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## Magical weights

By Ariel Marcy, 14 November 2023

Difficulty: Fun Ellen has a set of 6 weights that come in pairs. One pair is a magical set of negative weights (think helium balloons that take weight away). 2 of the weights are 1 kilogram each, 2 of the weights are 5 kilograms each, and the 2 magical weights are -3 kilograms each. Ellen […]

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## Nifty triangle numbers

By Ariel Marcy, 6 November 2023

Difficulty: Fun Triangular numbers are numbers that can be formed into a triangle. For example, 3 is a triangular number with 2 dots on the bottom row and 1 dot on top row forming an equilateral triangle of 3 dots. 6 is the next triangular number with 3 dots on the bottom, 2 dots in […]

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