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10: The price of wheat was >/bushel on January 2007 and $9/bushel on January 2008. By what percentage did the price change?

(a) 10%

　　(b) 40%

　　(c) 60%

　　(d) 80%

　　(e) 90%

Answer:

The price change is [(Price2008 - Price2007)/Price2007]·100 = [(9 - 5)/5]·100 = (4/5)·100 = 80%

11: In the figure below, angle AMB is 100o, angle BMD is 40o and angle CME is 60o. What is the value of angle CMD?

　　Figure not drawn to scale

　　(a) 20o

　　(b) 30o

　　(c) 40o

　　(d) 50o

　　(e) 80o

Answer:

If angle AMB is 100o, then angle BME is 180o - 100o = 80o

BMC + CMD = 40o

BMC + CMD + DME = 80o

If we subtract the 2 equations, DME = 40o

CMD + DME = 60o

BMC + CMD + DME = 80o

If we subtract the 2 equations, BMC = 20o

CMD = BME - BMC - DME = 80o - 40o - 20o = 20o

12: A vehicle runs from town A to town B at a speed of 20 miles/hour while another vehicle runs from town B to town A at a speed of 60 miles/hour. Both vehicles start their trips at the same time and the distance between towns is 100 miles. How long does it take from the time they start running to the moment they are at the same point on the road?

　　(a) 1 hour

　　(b) 1 hour and 15 minutes

　　(c) 1 hour and 30 minutes

　　(d) 1 hour and 45 minutes

　　(e) 2 hours and 15 minutes

100 miles = d1 + d2 This is equation #1.

It take the same time for the 2 cars to meet: t = d1/(20 miles/hour) = d2/(60miles/hour). This is equation #2.

We solve the system of 2 equations to find d1 and d2.

From equation #2, 3·d1 = d2.

Then 100 miles = d1 + d2 = 4·d1, so d1 = 25 miles and d2 = 75 miles.

The answer is t = d1/20miles/hour = 25/20 = 5/4 = 1 hour and 15 minutes.

延伸阅读：

SAT数学专项练习题（一）

SAT数学专项练习题（二）

SAT数学专项练习题（三）

更多阅读资料：
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