Stage: 3 Challenge Level: 
There are at least twelve solutions to the addition sum
| M | U | M | |
| + | D | A | D |
| -- | -- | -- | -- |
| K | I | D | S |
You have to replace the seven letters by seven numbers. How many solutions can you find? How many solutions are there?
Algorithms. Generalising. Patterned numbers. Addition & subtraction. Mathematical reasoning & proof. Multiplication & division. Positive-negative numbers. Place value. Working systematically. Properties of numbers.
Published March 2001.
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