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carl drove

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carl drove

by shibal » Sat May 16, 2009 12:31 pm
carl drove from his home to the beach in an avg speed of 80 km per hr and returned home at avg speed of 70 km/hr. he spent 1/2 hour longer to come back home. how many km did he drive each way?

OA: 280
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by truplayer256 » Sat May 16, 2009 12:38 pm
Average speed= total distance/total time.

Let's assume that the distance from Carl's home to the beach was y miles and that it took Carl x hours to travel those y miles when going to the beach. So:

y/x=80
x=y/80

The problem tells us that it took Carl 1/2 an hour longer when coming back home. So:

y/x+1/2=70
y=70x+35
Plug in x=y/80 and solve for y.
y=7y/8+35
y/8=35
y=280
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by artistocrat » Sat May 16, 2009 3:02 pm
S=D/T

80=D/x

70=D/(x+1/2)

D=D
80x=70x+35
10x=35
x=3.5

80*3.5=280
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