Question: In Johnstown, the population is 80 and every single person drives by themselves to work. Each car on a road pollutes 10 pounds of carbon a year. A single bus pollutes 100 pounds of carbon a year. A bus can hold 40 people. The town decides to start running a bus and 25% of the people who used to drive now take the bus. How many fewer pounds of carbon are now emitted per year? Think carefully first, then make a decision:
The town used to emit 800 pounds of carbon a year because 80 x 10 = 800. 20 now take the bus because 80 x .25 = 20. 60 people still drive because 80 - 20 = 60. Those 60 people create 600 pounds of carbon because 60 x 10 = 600. The town now emits 700 pounds of carbon because 100 + 600 = 700. The town emits 100 fewer pounds of carbon now because 800 - 700 = 100. So the answer is 100.