The table below shows the number of times the dishwasher was used in three different houses over three days. Dishwasher Use House AHouse BHouse CFriday122Saturday234Sunday223On Friday, 17.5 total gallons of water were used. On Saturday, 31.5 total gallons were used. On Sunday, 24.75 total gallons were used. What is the difference between the water use per load of the dishwasher that uses the most water and the dishwasher that uses the least water?

Let each house’s water use per load be its rate. Comparing Saturday’s total with Sunday’s gives House B’s rate plus House C’s rate: 31.5 − 24.75 = 6.75 gallons. Friday’s total then gives House A’s rate: 17.5 − 2(6.75) = 4 gallons. Using Sunday’s total, 2(4) + 2B + 3C = 24.75; together with B + C = 6.75, this gives B = 3.5 and C = 3.25 gallons per load. The difference between the greatest rate, 4 gallons, and the least, 3.25 gallons, is 0.75 gallon, choice B.

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