AMC12 2006 B
AMC12 2006 B · Q5
AMC12 2006 B · Q5. It mainly tests Linear equations, Rates (speed).
John is walking east at a speed of 3 miles per hour, while Bob is also walking east, but at a speed of 5 miles per hour. If Bob is now 1 mile west of John, how many minutes will it take for Bob to catch up to John?
John 以每小时 3 英里的速度向东走，而 Bob 也向东走，但速度为每小时 5 英里。如果 Bob 现在在 John 以西 1 英里处，Bob 追上 John 需要多少分钟？
(A)
30
30
(B)
50
50
(C)
60
60
(D)
90
90
(E)
120
120
Answer
Correct choice: (A)
正确答案：（A）
Solution
The speed that Bob is catching up to John is $5-3=2$ miles per hour. Since Bob is one mile behind John, it will take $\frac{1}{2} \Rightarrow \text{(A)}$ of an hour to catch up to John.
Bob 追赶 John 的相对速度是 $5-3=2$ 英里/小时。由于 Bob 落后 John 1 英里，追上所需时间为 $\frac{1}{2} \Rightarrow \text{(A)}$ 小时。
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