Question

Electricity costs $0.10 per kilowatt-hour. How does it cost a family each year if they use 250 kilowatt-hours per month?

Answer 1

Let's calculate how the electricity costs a family each year:

$$Cost = Rate\cdot E \cdot \dfrac{12\ month}{1\ year},$$ $$Cost = 0.10\ \dfrac{\$}{kWh}\cdot 250\ \dfrac{kWh}{month} \cdot \dfrac{12\ month}{1\ year}=300\ \dfrac{\$}{year}.$$

Answer:

$Cost = 300\ \dfrac{\$}{year}.$