SAT数学备考经典模拟题训练33

>>SAT数学模拟题：SAT数学备考经典模拟题训练33

>>SAT考试辅导

· Question #6: A bus travels from town A to town B for 2 hours at a speed of 60 miles/hour. The bus stops in town B for 2 hours and then travels from town B to town C for 1 hour, at a speed of 50 miles/hour. What is the average speed of the bus?

(a) 30miles/hour

(b) 31miles/hour

(c) 32miles/hour

(d) 34miles/hour

(e) 40miles/hour

解析

o Answer: The circumference of the circle is 2·¶·r = 2·¶·10/¶ = 20.

The ratio between the length of arc AB and the circumference of the circle is equal between the ratio between the 45o angle and 360o.

In conclusion, AB = 20 · 45o/360o = 20/8 = 5/2.

o Answer: The distance the bus travels from A to B is 60 miles/hour · 2 hours = 120 miles.

Then, the bus travels from B to C: 50 miles/hour · 1 hour = 50 miles.

The total distance traveled is 120 + 50 = 170 miles and the total time is 2 hours + 2 hours stop + 1 hour = 5 hours.

In conclusion the average speed was 170 miles / 5 hours = 34 miles/hour.

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