Stage: 3 Challenge Level: 
We have exactly $100$ coins. There are five different values of coins.
We have decided to buy a piece of computer software for $39.75$. We have the correct money, not a penny more, not a penny less!
Can you discover what the five different types of coins are worth and how many of each we have saved?
Mathematical reasoning & proof. Coins. Visualising. Generalising. Money. Algebra - generally. Number theory. Creating expressions/formulae. Number - generally. Networks/Graph Theory.
Published October 2001.
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