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Car X traveled from City A to city B in 30 minutes ...

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Car X traveled from City A to city B in 30 minutes ...

by doclkk » Fri Jul 03, 2009 9:20 am
Car X traveled from City A to city B in 30 minutes. What was the avg speed of car X

1. Half the distance of the trip was covered at 50 mph and the other half of the distance was covered at 60 mph

2. Car X traveled 30 miles during the trip

My guess A

OA: D (question is from GMAT express application on iPhone)

My thoughts - 2 does not say anything about speed or time. How on earth does 2 help us.
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Re: Car X traveled from City A to city B in 30 minutes ...

by cata1yst » Fri Jul 03, 2009 9:25 am
doclkk wrote:Car X traveled from City A to city B in 30 minutes. What was the avg speed of car X

1. Half the distance of the trip was covered at 50 mph and the other half of the distance was covered at 60 mph

2. Car X traveled 30 miles during the trip

My guess A

OA: D (question is from GMAT express application on iPhone)

My thoughts - 2 does not say anything about speed or time. How on earth does 2 help us.
d = r * t
30 = r * .5
60 = r

1 and 2 are SUFFICIENT so D.
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Re: Car X traveled from City A to city B in 30 minutes ...

by El Cucu » Fri Jul 03, 2009 11:35 am
doclkk wrote:Car X traveled from City A to city B in 30 minutes. What was the avg speed of car X

1. Half the distance of the trip was covered at 50 mph and the other half of the distance was covered at 60 mph

2. Car X traveled 30 miles during the trip

My guess A

OA: D (question is from GMAT express application on iPhone)

My thoughts - 2 does not say anything about speed or time. How on earth does 2 help us.
IMO D). from 1) you can make one equation with one unknown sufficient
from 2) idem if you know the distance + time (given in the question) you can know the avg
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by Umar82 » Thu Jul 23, 2009 7:27 am
Could someone please write out the formula for statement 1?

Thanks!
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by El Cucu » Thu Jul 23, 2009 8:02 am
Umar82 wrote:Could someone please write out the formula for statement 1?

Thanks!
Car X traveled from City A to city B in 30 minutes. What was the avg speed of car X

1. Half the distance of the trip was covered at 50 mph and the other half of the distance was covered at 60 mph

2. Car X traveled 30 miles during the trip

1) x/50+x/60= 2x/y

note that x/50 is distance/speed=time
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by ogbeni » Thu Jul 23, 2009 1:29 pm
From statement1, can't we just take the average of the 1st half and second half to get average speed instead of applying a formula? Does the question have to read ". Half the distance of the trip was covered at [a constant speed of] 50 mph and the other half of the distance was covered at [a constant speed of] 60 mph " - Note my addition of the word constant speed. I still feel that if constant were not added you can still take the average of both and 1 would be sufficient

Any thoughts?
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