Question

1.    A 300 W plasma TV is used for 30 hours in a week, and costs 81p to run. How much is the unit cost of electricity?

Answer 1

$$E=Pt=300\ W\cdot30\ h=9\ kWh.$$ $$Unit\ Cost=\dfrac{81\ p}{9\ kWh}=9.0\ \dfrac{p}{kWh}.$$