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A past puzzle

By David, 26 August 2020 Brainteaser

Painting of boys in a classroom working out a maths question on the black board.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:

(102 + 112 + 122 + 132 + 142) ÷ 365

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

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Brainteaser hint

• Although the kids in the painting are trying to do it in their heads, you can always use a pencil!
• Remember that teachers often like questions with nice round answers.
• 102 means 10 x 10. Calculate these first!

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Brainteaser answer

The answer is 2.

Here’s the working:
answer = (102 + 112 + 122 + 132 + 142) ÷ 365 = (100 + 121 + 144 + 169 + 196) ÷ 365 = 730 ÷ 365 = 2

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