The teachers' room has a coffee maker. Usually five days a week, twice a day, someone makes coffee in the break time, has one cup, then the rest of the coffee sits in the pot, with the heater on, for 90 minutes until the next lesson has finished. The coffee maker uses a 1 kW heating element to keep the coffee warm.
There is a new coffee machine with a thermos flask pot, and no heating element.
It costs 10,000 yen.
Electricity costs 25 yen per kWh
If we buy the new coffee machine, how many weeks will it take to save the money?
