Mary used 15 gallons of fuel this week. Last week she used 20% less. How much fuel did she use in total for the two weeks?
Last week, she used 15 gallons * 0.2 = <T>multiply(15, 0.2)=3.0 gallons less fuel than she used this week.
This means that she used 15 gallons – 3 gallons = <T>subtract(15, 3)=12 gallons of fuel last week.
In total, Mary used 15 gallons + 12 gallons = <T>add(15, 12)=27 gallons of fuel.
