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The tail of a 1-mile long train exits a tunnel exactly 3 minutes after the front of the train entered the tunnel. If the train is moving 60 miles per hour, how long is the tunnel?

 

Why is this wrong???

 

Let d be the length of the tunnel. Let the time that the train goes through this tunnel be t. Then d/t = 60, so d = 60t.

The train goes through d + 1 miles in t + 3/60 hours. So (d + 1)/60 = t + 3/60.

 

But this is wrong since it has no solutions. Why?!?!

 Jan 17, 2021
edited by Guest  Jan 17, 2021
 #1
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When the front of the train enters, the tail has 1 mile to go to enter

(1 mile + length of tunnel ) / 60 = 3/60 hr         (3/60 hr = 3 minutes)

tunnel length = 2 miles

 Jan 17, 2021
 #2
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You're not using that it exits 3 minutes after the front has entered it...

 

The time it takes the front to go from the start of the tunnel to the end is d/60...

Guest Jan 17, 2021

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