If the car had traveled 20kmph faster than it actually did,

Oldest

Best Reply

Author

Message

TAGS:

CEO

Joined: 29 Mar 2007

Posts: 2618

Followers: 13

Kudos [?]: 145 [0], given: 0

If the car had traveled 20kmph faster than it actually did, [#permalink]

25 Oct 2007, 15:34

If the car had traveled 20kmph faster than it actually did, the trip would have lasted 30minutes less. If the car went exactly 60km, what speed did it travel?

Here is my equation and I can't get to the right answer... Where am I making the mistake?

(R+20)(t-1/2)=60

Rt=60

Rt-1/2R+20t -10 =60 ---> Rt-1/2R+20t=70

60-1/2R+20t=70 ---> -1/2R+20t=10 (t=60/R)

-1/2R+20(60/R)=10 ---> 1200/R-R/2=10 --> (2400-R^2)/2R=10

2400-R^2=20R ---> R^2-20R-2400=0 (R-60)(R+40)=0

So R= 60... OA is 40.... what am I doing wrong?

Director

Joined: 03 May 2007

Posts: 903

Schools: University of Chicago, Wharton School

Followers: 4

Kudos [?]: 30 [0], given: 6

Re: Challenges Rate [#permalink]

25 Oct 2007, 19:00

GMATBLACKBELT wrote:

If the car had traveled 20kmph faster than it actually did, the trip would have lasted 30minutes less. If the car went exactly 60km, what speed did it travel?

Here is my equation and I can't get to the right answer... Where am I making the mistake?

(R+20)(t-1/2)=60

Rt=60

Rt-1/2R+20t -10 =60 ---> Rt-1/2R+20t=70

60-1/2R+20t=70 ---> -1/2R+20t=10 (t=60/R)

-1/2R+20(60/R)=10 ---> 1200/R-R/2=10 --> (2400-R^2)/2R=10

2400-R^2=20R ---> R^2 - 20R-2400=0
(R-60)(R+40)=0

So R= 60... OA is 40.... what am I doing wrong?

2400 - R^2 = 20R
R^2 + 20R - 2400 = 0
(R + 60)(R - 40)=0
R = 40

CEO

Joined: 29 Mar 2007

Posts: 2618

Followers: 13

Kudos [?]: 145 [0], given: 0

Re: Challenges Rate [#permalink]

25 Oct 2007, 21:08

Fistail wrote:

GMATBLACKBELT wrote:

If the car had traveled 20kmph faster than it actually did, the trip would have lasted 30minutes less. If the car went exactly 60km, what speed did it travel?

Here is my equation and I can't get to the right answer... Where am I making the mistake?

(R+20)(t-1/2)=60

Rt=60

Rt-1/2R+20t -10 =60 ---> Rt-1/2R+20t=70

60-1/2R+20t=70 ---> -1/2R+20t=10 (t=60/R)

-1/2R+20(60/R)=10 ---> 1200/R-R/2=10 --> (2400-R^2)/2R=10

2400-R^2=20R ---> R^2 - 20R-2400=0
(R-60)(R+40)=0

So R= 60... OA is 40.... what am I doing wrong?

2400 - R^2 = 20R
R^2 + 20R - 2400 = 0
(R + 60)(R - 40)=0
R = 40

I knew it was something so simple, but I just couldn't snuff it out.

Thx

Re: Challenges Rate [#permalink] 25 Oct 2007, 21:08

		Similar topics	Author	Replies	Last post
Similar Topics:		A train can travel 20% faster than a car. Both start from a	BG	1	23 Mar 2004, 01:55
		How much time did it take a certain car to travel 400	kuristar	6	19 Jun 2006, 10:07
		How much time did it take a certain car to travel 400	tarek99	9	25 Jan 2008, 06:56
		How much time did it take a certain car to travel 400	GHIBI	4	30 Jan 2008, 08:59
	1	How much time did it take a certain car to travel 400	enigma123	4	13 Nov 2011, 02:19

If the car had traveled 20kmph faster than it actually did,

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

If the car had traveled 20kmph faster than it actually did,

If the car had traveled 20kmph faster than it actually did,

Main navigation

GMAT Resources

Partners

MBA Resources