Stage: 3 Challenge Level: 
In the following sum the letters A, B, C, D, E and F stand for six distinct digits. Find all the ways of replacing the letters with digits so that the arithmetic is correct.
Addition & subtraction. Visualising. Creating expressions/formulae. Properties of numbers. Mathematical reasoning & proof. Integers. Number - generally. Combinatorics. Generalising. Working systematically.
Published October 2001.
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