mscroggs.co.uk
mscroggs.co.uk

subscribe

# Sunday Afternoon Maths LVI

## Archive

Show me a Random Puzzle
▼ show ▼
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 LXI,
puzzles about triangle numbers, or a random puzzle.