greenwich 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.
Statement 1:
Case 1: Car Y starts at 6:00:10 and finishes at 6:00:15, for a total time of 5 seconds.
Since Car X starts 3 seconds after Car Y and finishes 2 seconds after Car Y, Car X starts at 6:00:13 and finishes at 6:00:17, for a total time of 4 seconds.
Case 2: Car Y starts at 6:00:10 and finishes at 6:00:20, for a total time of 10 seconds.
Since Car X starts 3 seconds after Car Y and finishes 2 seconds after Car Y, Car X starts at 6:00:13 and finishes at 6:00:22, for a total time of 9 seconds.
Since Car X's time can be different values, INSUFFICIENT.
The cases above illustrate the following relationship between Car X's time and Car Y's time:
Car X's time is 1 second less than Car Y's time.
Statement 2:
Thus, Car Y's time = d/r = (1/2)/(30) = 1/60 of an hour = 1 minute = 60 seconds.
No way to determine Car X's time.
Statements combined:
Since Car Y's time = 60 seconds, and Car X's time is 1 second less, Car X's time = 60-1 = 59 seconds.
SUFFICIENT.
The correct answer is
C.
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