*"Why do we have 1p and 2p coins? There's nothing that only costs a penny or tuppence these days!"*

*"We need them, to make sure we can make all of the bigger amounts!"*

*"Well couldn't we do that with some bigger coins?"*

*"If we only had 3p and 7p coins, there'd be some values that we couldn't make, like 4p or 8p!"*

*"Yes, but I reckon we'd be able to make most amounts, even if we only had 3p and 7p coins..."*

**Which values is it impossible to make with 3p and 7p coins?**

Given an amount, is there a quick way to work out how to make it?

**Given an amount, is there a quick way to work out how to make it with the least number of coins?**