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PS Question 55.3.13

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PS Question 55.3.13

by maxxwe11 » Thu Sep 17, 2009 7:01 pm
The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car A's average speed was 10 miles per hour greater than that of car B, what was car B's average speed, in miles per hour?

a. 20
b. 30
c. 40
d. 50
e. 80

_____________________________

I eventually got the right answer on this one, but it took me longer than 2 minutes. I was wondering if there was a quick(er) way to set this up.

Thanks!
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by blr_gmat_prep » Thu Sep 17, 2009 9:27 pm
Car B Avg Speed (from options) :20,30,40,50,60
Car A Avg Speed (As mentioned): 30,40,50,60,70


Given that

400/B = 400/A +2 ---(1)

Starting with middle value , so that we know if we have to go up or down.

400/40 = 10
400/50 = 8
=> 8+2 = 10 --(1) is satisfied.
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Re: PS Question 55.3.13

by fruti_yum » Sat Sep 19, 2009 7:06 am
maxxwe11 wrote:The time it took car A to travel 400 miles was 2 hours less than the time it took car B to travel the same distance. If car A's average speed was 10 miles per hour greater than that of car B, what was car B's average speed, in miles per hour?

a. 20
b. 30
c. 40
d. 50
e. 80

_____________________________

I eventually got the right answer on this one, but it took me longer than 2 minutes. I was wondering if there was a quick(er) way to set this up.

Thanks!
Is it C? I just took the manhattan gmat approach.. avg = totoal distance/ total time! and calculated each one like a word problem..
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