如果这是一张纸，你是在现场的，你可以在这张纸的背面提交你的答案。请把你的名字写在背面的最上面，并在你计算的数字上编号，从1到4。
If this is a piece of paper, you are Live, and you can submit your answers on the back of this piece of paper. Please put your name at the top of the back and number your calculations from 1 through 4.

如果这是一个电脑屏幕，那你就是电子方式的，你可以按照老师的建议提交答案。请把你的名字和问题的编号(1，2，3或4)写在提交答案的每个问题的上面。
If this is a computer screen, you are Electric, and you can submit your answers to your teacher as your teacher directs. Please put your name and the number of the problem (1, 2, 3 or 4) at the top of each problem you submit answers for.

数学问题4 - 读完上面的说明后，也许你会想要用太阳能板来驱动一辆汽车，就像麻省理工学院的孩子们在他们的年度比赛中所做的那样。但经过一番了解，你发现太阳能电池板的价格要比你爸爸愿意花的500美元还贵，而且还需要一个电动马达。尽管如此，你还是喜欢这样的想法：一旦开始开车，你就不用再花油钱了。幸运的是,有人告诉你：柴油发动机可以使用清洁的厨房油脂。而且你爸开的正是柴油皮卡,你发现使用厨房油脂的话可以省下900美元，最多在启程和结束阶段需要用一点柴油。你还了解到，你经常去的汉堡店每月要花35美元来处理掉50加仑的桶装油脂，而且因为你是顾客，他们马上会付钱给你。最主要的问题是说服你爸。假设他的年行驶里程是1万英里，每加仑汽油能跑15英里，而柴油的年均价格是3美元，计算一下需要多长时间才能让改装工具收回成本。用年的形式来回答，折算掉月、周、小时等部分。假设你算出来是半年时间，请说明你是如何得出这个结论的。
Math Problem 4 - After reading the note above, maybe you wonder about using solar panels to make a car go, like the kids at MIT do in their annual contest. But after some checking, you find that solar panels would cost more than the $500 your dad is willing to spend, plus of course he’d need an electric motor. Still, you like the idea of not having to ask for gas money once you start driving. Luckily, somebody told you about how diesel motors can run on clean used kitchen grease, and since your dad drives a diesel pickup, you have found out that for about $900 you could convert your dad’s pickup to run on used grease, and that after that he wouldn’t have to use diesel fuel except at the very beginning and very end of each trip. You've also learned that the burger joint you go to all the time has to pay $35/month to have their 50 gallon barrel of grease drained each month, and that they'd just as soon pay you since you're a customer. The chief problem is selling dad. Assuming his annual milage is 10,000 and he gets 15 miles per gallon at a time when diesel costs $3 all year long, figure out how long it would take to make the conversion kit pay for itself. Answer in the form of years, spelling out any fractional portion as months, weeks, hours, etc. Assuming you figured about half a year, show how you arrived at this conclusion.

可能需要的时间:10分钟。
Likely time to solve: 10 min.

成绩单上的计分:算术 7
What counts on the report card: Arithmetic 7