AMC12 2007 A
AMC12 2007 A · Q4
AMC12 2007 A · Q4. It mainly tests Averages (mean), Rates (speed).
Kate rode her bicycle for 30 minutes at a speed of 16 mph, then walked for 90 minutes at a speed of 4 mph. What was her overall average speed in miles per hour?
Kate先以$16$ mph的速度骑自行车$30$分钟，然后以$4$ mph的速度步行$90$分钟。她的总体平均速度是多少（单位：英里/小时）？
(A)
7
7
(B)
9
9
(C)
10
10
(D)
12
12
(E)
14
14
Answer
Correct choice: (A)
正确答案：（A）
Solution
\[16 \cdot \frac{30}{60}+4\cdot\frac{90}{60}=14\]
\[\frac{14}2=7\Rightarrow\boxed{A}\]
\[16 \cdot \frac{30}{60}+4\cdot\frac{90}{60}=14\]
\[\frac{14}2=7\Rightarrow\boxed{A}\]
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