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Average Rates problem

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Average Rates problem

by anuptvm » Wed Dec 29, 2010 6:19 am
On a trip from A to B, Julio drove the first x miles at 50 mph and the remaining distance at 60 mph. How long did it take Julio to drive the first x miles?

(1) On this trip, Julio drove for a total of 10 hours and drove a total of 530 miles

(2) On this trip, it took Julio 4 more hours to drive the first x miles than to drive the remaining distance.

My answer was C but OA is A

Could someone explain
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Source: — Data Sufficiency |
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by Night reader » Wed Dec 29, 2010 6:29 am
anuptvm wrote:On a trip from A to B, Julio drove the first x miles at 50 mph and the remaining distance at 60 mph. How long did it take Julio to drive the first x miles?

(1) On this trip, Julio drove for a total of 10 hours and drove a total of 530 miles

(2) On this trip, it took Julio 4 more hours to drive the first x miles than to drive the remaining distance.

My answer was C but OA is A

Could someone explain
fairly easy DS

let's d=total distance

st(1) x/50 (time spent for driving x miles) + (d-x)/60 (time for remaining distance) = 10 and d= 530 => solve for x. Sufficient
st(2) x/50 = (d-x)/60 + 4 (hours) => one equation and two variables. Not Sufficient

Answer: A
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by gmat7202011 » Thu Dec 30, 2010 1:05 pm
Let x be the time taken by him @ 50

Since Speed x Time = Distance

50 x + 60*(10-x) = 530

x can be deduced from this.
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by MAAJ » Fri Dec 31, 2010 6:53 am
(1) On this trip, Julio drove for a total of 10 hours and drove a total of 530 miles

50t1 + 60t2 = 530
t1 + t2 = 10

Sufficient!

(2) On this trip, it took Julio 4 more hours to drive the first x miles than to drive the remaining distance.

50t1 + 60t2 = ?
50x + 60(x-4) = ?

Not Sufficient!

Answer is A
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