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Sunday Afternoon Maths LVI

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Posted on 2016-10-23

Blackboard Sums II

The numbers 1 to 20 are written on a blackboard. Each turn, you may erase two adjacent numbers, $$a$$ and $$b$$ ($$a$$ is to the left of $$b$$) and write the difference $$a-b$$ in their place. You continue until only one number remains.
What is the largest number you can make?
Tags: Numbers

An Arm and a Leg

If 60% of people have lost an eye, 75% an ear, 80% an arm and 85% a leg, what is the least percentage of people that have lost all four?
If you enjoyed these puzzles, check out Sunday Afternoon Maths LIX,
puzzles about chalkdust crossnumber, or a random puzzle.