A collector has a thousand silver coins that you want to clean. To do so, he goes to a store to buy as much cleaning product as necessary.
- How much will the product cost me to clean a thousand silver coins? - I ask.
- That will cost two hundred and fifty silver coins - replied the shopkeeper.
- Well, then I don't need to clean them all - replied the collector.
Do you know how many silver coins the collector paid to be able to clean the rest of the coins knowing that there was nothing left of the cleaning product?
The collector finished with 800 glittering coins since with the other 200 He paid for the cleaning product since it is deduced from the statement that by spending one coin he can clean another four.