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OG 12 | WORD PROBLEMS

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OG 12 | WORD PROBLEMS

by [email protected] » Thu Oct 04, 2012 6:19 pm
If Car X followed Car Y across a certain bridge that is
1/2 mile long, how many seconds did it take Car X to
travel across the bridge?

(1) Car X drove onto the bridge exactly 3 seconds
after Car Y drove onto the bridge and drove off
the bridge exactly 2 seconds after Car Y drove
off the bridge.
(2) Car Y traveled across the bridge at a constant
speed of 30 miles per hour.

Cant understand the first statement!
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Source: — Data Sufficiency |
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by GMAT Kolaveri » Thu Oct 04, 2012 6:36 pm
Question stem: how many seconds did it take Car x to travel across the bridge?

We need to find a value for the time Car x took to travel across that bridge. We have the distance (1/2 mile) We need the speed of Car X.

Statement 2: Says about the speed of Y. NOT SUFFICIENT.
Statement 1: Car X drove after 3 seconds and left before 2 seconds. Which means that Car X took 1 second less than the time take by Car Y. This statement gives the relation between the time taken by Car X and Car Y. But we cannot calculate the time taken by Car Y with this statement alone. NOT SUFFICIENT.

Taking both the statement, we can calculate the time taken by Car Y (from st 2) and from time taken by Y we can calculate the time taken by Car X.

OA: C
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by Anurag@Gurome » Thu Oct 04, 2012 9:12 pm
[email protected] wrote:If Car X followed Car Y across a certain bridge that is
1/2 mile long, how many seconds did it take Car X to
travel across the bridge?

(1) Car X drove onto the bridge exactly 3 seconds
after Car Y drove onto the bridge and drove off
the bridge exactly 2 seconds after Car Y drove
off the bridge.
(2) Car Y traveled across the bridge at a constant
speed of 30 miles per hour.

Cant understand the first statement!
Let the time needed for car X to travel across the bridge be Tx seconds and the time for Y be Ty seconds.
We have to find Tx.

(1) Car X drove onto the bridge exactly 3 seconds after car Y drove onto the bridge and drove off the bridge exactly 2 seconds after car Y drove off the bridge.
Car X needs 1 second less to travel across the bridge than car Y implies Ty = Tx + 1, but we cannot find Tx from this; NOT sufficient.

(2) Car Y traveled across the bridge at a constant speed of 30 miles per hour implies 30/3600 = 1/120 miles per second.
Car Y needs Ty = 21/(1/120) = 21 * 120 seconds to travel across the bridge, but we cannot find Tx from this; NOT sufficient.

Combining (1) and (2), Ty = Tx + 1 and Ty = 21 * 120
Tx = (21 * 120) - 1; SUFFICIENT.

The correct answer is C.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

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