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Blackboard sums

The numbers 1 to 20 are written on a blackboard. Each turn, you may erase two numbers, \(a\) and \(b\) and write the sum \(a+b\) in their place. You continue until only one number remains.
What is the largest number you can make?

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Tags: numbers
If you enjoyed this puzzle, check out Sunday Afternoon Maths LV,
puzzles about numbers, or a random puzzle.

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