In the subtraction calculation below, each of the letters K, A, N, G, R and O represents a different digit.

$\ \$ K A N
- G A R
$\ \ \ \ \$ O O

What is the largest possible value of the number 'KAN'?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.

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