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Bus

by crackgmat007 » Tue Sep 29, 2009 5:52 pm
To arrive at its destination on time, a bus should have maintained a speed of V kmh throughout its journey. Instead, after going the first third of the distance at V kmh, the bus increased its speed and went the rest of the distance at (1.2)*V kmh. If, as a result, the bus arrived at its destination X minutes earlier than planned, what was the actual duration of the trip?

1. V = 60
2. X = 20

OA - B
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by vaibhav.iit2002 » Wed Sep 30, 2009 7:15 am
Say original planned duration = t and total distance=a

now t=a/v ...1

for 1/3rd distance, time taken=(a/3)/v
for remaining 2/3rd distance, time taken=(2a/3)/1.2v

hence t-x=(a/3)/v + (2a/3)/1.2v ....2

from 1 and 2,
t-x=t/3 + 2t/(3x1.2)

hence we need x to get value of t.

Hence B.
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