the destination of Donald?

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Sat Feb 08, 2014 2:08 am

Donald is driving at a given speed, which if quartered; it would take him 3 hours longer to reach the destination than what is the normal time. How long in miles is the destination of Donald?
(1) It would take Donald 1 hour to reach his destination if he drives at the given speed.
(2) The difference in the given and the quartered speeds of Donald is 60 miles per hour.

Made Up

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
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The Princeton Review - Manya Abroad
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Source: Beat The GMAT — Data Sufficiency | Sat Feb 08, 2014 2:08 am

Bill@VeritasPrep: GMAT Instructor; Posts: 1248; Joined: Thu Mar 29, 2012 2:57 pmFollowed by: 192 members; Location: Everywhere; Thanked: 503 times; GMAT Score:780

by Bill@VeritasPrep » Sat Feb 08, 2014 8:14 pm

sanju09 wrote:Donald is driving at a given speed, which if quartered; it would take him 3 hours longer to reach the destination than what is the normal time. How long in miles is the destination of Donald?
(1) It would take Donald 1 hour to reach his destination if he drives at the given speed.
(2) The difference in the given and the quartered speeds of Donald is 60 miles per hour.

Made Up

From the stem:

Normal speed:

D=RT

Reduced speed:

D=(R/4)(T+3)

D=(RT+3R)/4

4D=RT + 3R

4D - 3R = RT

Plug into the normal speed equation:

D = 4D - 3R

3D = 3R

D = R

Statement 1 tells us that T = 1, so in D=RT, D=R, which we already knew from the question stem. No new info means it's not sufficient, so eliminate A and D, and you can also eliminate C because adding it to Statement 2 won't help.

Statement 2 tells us that R - R/4 = 60, which we can solve:

R - R/4 = 60

4R/4 - R/4 = 60

3R/4 = 60

3R = 240

R=80

Since we know that D = R, then D = 80 as well. Sufficient.

B

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Mon Feb 10, 2014 10:26 pm

Bill@VeritasPrep wrote:
sanju09 wrote:Donald is driving at a given speed, which if quartered; it would take him 3 hours longer to reach the destination than what is the normal time. How long in miles is the destination of Donald?
(1) It would take Donald 1 hour to reach his destination if he drives at the given speed.
(2) The difference in the given and the quartered speeds of Donald is 60 miles per hour.

Made Up
From the stem:

Normal speed:

D=RT

Reduced speed:

D=(R/4)(T+3)

D=(RT+3R)/4

4D=RT + 3R

4D - 3R = RT

Plug into the normal speed equation:

D = 4D - 3R

3D = 3R

D = R

Statement 1 tells us that T = 1, so in D=RT, D=R, which we already knew from the question stem. No new info means it's not sufficient, so eliminate A and D, and you can also eliminate C because adding it to Statement 2 won't help.

Statement 2 tells us that R - R/4 = 60, which we can solve:

R - R/4 = 60

4R/4 - R/4 = 60

3R/4 = 60

3R = 240

R=80

Since we know that D = R, then D = 80 as well. Sufficient.

B

Perfect! Looking for a shorter elucidation.

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

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