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by colakumarfanta » Fri May 21, 2010 3:07 am
A and B start moving in opposite direction . A starts a 9 pm and B starts at 6 pm . A's speed is 40 m/hr and B's speed is 20m/hr . What is the time when they are 240 miles apart .
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by liferocks » Fri May 21, 2010 3:40 am
Question does not mention one important point,weather A and B started from same point and moved towards each other or away from each other.
If I assume A and B started from same point and moved away from each other,
At 9pm distance between them 3*20=60 miles
from 9pm relative speed is 40+20=60,iles per hour
so they will be 240miles apart in another (240-60)/60=3hr or at 12am
"If you don't know where you are going, any road will get you there."
Lewis Carroll
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by gmatjedi » Fri May 21, 2010 3:36 pm
d=rt
since b starts 3 hrs earlier than a, t=t+3
since a starts 3 hrs after b, t=t
For B,
x=20(t+3)

For A,
240-x=40t

240 -[20(t+3)]=40t
t=3 hrs
so 3 hrs from when A leaves = time to 240 mi apart
or
6 hrs (t+3) from when B leaves= time to 240 mi apart
=12a
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