SAT数学Problem Solving练习题（39）

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以下是易伯华SAT频道为大家整理了SAT数学Problem Solving练习题(39)，供考生们参考，以下是详细内容。

Question 39: 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.