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# A train takes 15 seconds to cross a bridge at 50 mph, and at

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A train takes 15 seconds to cross a bridge at 50 mph, and at [#permalink]  30 Apr 2019, 01:26
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Question Stats:

20% (02:55) correct 80% (01:59) wrong based on 5 sessions
A train takes 15 seconds to cross a bridge at 50 mph, and at the same speed takes 10 seconds to cross the same bridge when the train's length is halved.

 Quantity A Quantity B Length of the bridge Original length of the train

A)The quantity in Column A is greater.
B)The quantity in Column B is greater.
C)The two quantities are equal.
D)The relationship cannot be determined from the information given.
[Reveal] Spoiler: OA

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Re: A train takes 15 seconds to cross a bridge at 50 mph, and at [#permalink]  02 May 2019, 11:08
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Solutions for this problem please?
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Kudos [?]: 1253 [0], given: 5951

Re: A train takes 15 seconds to cross a bridge at 50 mph, and at [#permalink]  03 May 2019, 01:42
Expert's post
Recall the key formula

Distance = speed * time

Now, we do have actually two distances.

Let the bridge being B and the train is L

The common factor here is the speed = 50

1) $$\frac{B+L}{15} = 50$$

$$\frac{B+\frac{L}{2}}{10} = 50$$

Equate the two $$\frac{B+L}{15} = \frac{B+\frac{L}{2}}{10}$$

$$2(B + L) = 3(B + \frac{L}{2})$$

$$2B + 2L = 3B + \frac{3L}{2}$$

$$\frac{L}{2} = B$$

$$L = 2B$$

The length of the train is twice the length of the bridge.

Regards
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Re: A train takes 15 seconds to cross a bridge at 50 mph, and at   [#permalink] 03 May 2019, 01:42
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# A train takes 15 seconds to cross a bridge at 50 mph, and at

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