Question. 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?
Answer. 27
What step-by-step reasoning justifies that answer?
Reasoning: Last week, she used 15 gallons * 0.2 = 3 gallons less fuel than she used this week. This means that she used 15 gallons – 3 gallons = 12 gallons of fuel last week. In total, Mary used 15 gallons + 12 gallons = 27 gallons of fuel.