How it works
Sam went to the market with four pretend coins. Three stalls sold the same bag of apples.
Corner charged five coins, Hill three coins and Lake six coins. The same bag had three prices.
The bags were all the same size, so the cheapest bag was the best buy. That was Hill, the one stall that four coins could pay.
Sam paid three coins and kept one. Looking at prices first got the apples and a coin to spare.