By Rok Willesee

Difficulty: Tricky

A scientist was looking back at notes they made about their experiments. Unfortunately, in one experiment the scales didn’t work. Can you help them work out what the weight should be in the final experiment?

Four scales in a row. The first has a triangle and a circle on it and weighs 3, the second has a triangle and a square and weighs 5, the third has two squares and weighs 8 and the fourth has a triangle, a circle and a square and no weight measured.

Credit: CSIRO/Diya Dhaliwal


You can assume that two objects that are the same shape weigh the same amount.

Scroll down or click for a hint, or the answer!

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Brainteaser hint

First, see if you can work out what one square weighs.

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Brainteaser answer

The third scale has two squares and weighs 8. That means one square must weigh half of 8, which is 4.

The second scale has a triangle and square and weighs 5. If the square weighs 4, the triangle must weigh 1.

The first scale has a triangle and circle and weighs 3. If the triangle weighs 1, then the circle must weigh 2.

The final scale has a square, circle and triangle. The square weighs 4, the circle weighs 2 and the triangle weighs 1 for a total of 7.

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