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Senior Manager
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John traveled 80% of the way from Yellow-town to [#permalink]
 05 Apr 2006, 01:49
Question Stats:
100% (04:50) correct
0% (00:00) wrong based on 1 sessions
John traveled 80% of the way from Yellow-town to Green-fields by train at an average speed of 80 miles per hour. The rest of the way John traveled by car at an average speed of v miles per hour. If the average speed for the entire trip was 60 miles per hour, what is v in miles per hour?
(a) 30
(b) 40
(c) 50
(d) 55
(e) 70
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Director
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The average speed for the entire trip= Total distance/Total time
60/60=D/T
D/T=1
Pick 100 km for D...
This would yield T=100 minutes
Using the question stem we calculate 80 km were traveled in 1h (or 60 minutes)....
This leaves us with 40 minutes (2/3 of an hour) to travel 20km.....
R*T=D
R*2/3=20
R=30
Answer A....
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Manager
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A.
Let "100" be the total distance travel (D). Thus, D1 = 80 and D2 = 20.
V1 = 80 mph, V2 is the unknown, and total velocity (V) = 60 mph.
D1/V1 + D2/V2 = D/V
80/80 + 20/V2 = 100/60
20/V2 = 2/3
20 (3/2) = V2
30 = V2
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GMAT Club Legend
Joined: 07 Jul 2004
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let total distance be d
First part by train took 0.8d/80 = 0.01 hour
Last part of journey took 0.2d/v hours
average speed = 80dv/(0.8vd + 16d) = 60
80vd = 48vd + 960d
32vd = 960
vd = 30d
v = 30
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Senior Manager
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A 30 m/hr
if we consider total distance to be x and time taken as t.
(0.8x/80)+(0.2x)/v = (x/60)
=> v = 30
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