Average Rates problem

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anuptvm: Senior | Next Rank: 100 Posts; Posts: 52; Joined: Wed Aug 12, 2009 8:05 amFollowed by: 1 member; GMAT Score:650

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: Beat The GMAT — Data Sufficiency | Wed Dec 29, 2010 6:19 am

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

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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gmat7202011: Senior | Next Rank: 100 Posts; Posts: 56; Joined: Sat Dec 11, 2010 2:39 pm; Thanked: 3 times

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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MAAJ: Master | Next Rank: 500 Posts; Posts: 243; Joined: Sun Jul 12, 2009 7:12 amFollowed by: 2 members; Location: Dominican Republic; Thanked: 31 times; GMAT Score:480

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

"There's a difference between interest and commitment. When you're interested in doing something, you do it only when circumstance permit. When you're committed to something, you accept no excuses, only results."

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