A worker can load 1 full truck in 6 hours. A second worker..

Expert replies

AAPL: Moderator; Posts: 2632; Joined: Sun Oct 29, 2017 2:08 pmFollowed by: 2 members

by AAPL » Tue Feb 20, 2018 6:25 am

A worker can load 1 full truck in 6 hours. A second worker can load the same truck in 7 hours. If both workers load one truck simultaneously while maintaining their constant rates, approximately how long, in hours, will it take them to fill 1 truck?

A. 0.15
B. 0.31
C. 2.47
D. 3.23
E. 3.25

The OA is D.

First worker rate will be, 1/6 truck per hour.

Second worker rate will be, 1/7 truck per hour.

Then, their combined rates if they working together will be, 1/T = 1/6+1/7. Then T = (6*7)/(6+7) = 42/13 = 3.23 hours.

Is there a strategic approach to this PS question? Can any experts help, please? Thanks!

Like this post

Source: Beat The GMAT — Problem Solving | Tue Feb 20, 2018 6:25 am

DavidG@VeritasPrep: Legendary Member; Posts: 2663; Joined: Wed Jan 14, 2015 8:25 amFollowed by: 128 members; Location: Boston, MA; Thanked: 1153 times; GMAT Score:770

by DavidG@VeritasPrep » Tue Feb 20, 2018 7:43 am

AAPL wrote:A worker can load 1 full truck in 6 hours. A second worker can load the same truck in 7 hours. If both workers load one truck simultaneously while maintaining their constant rates, approximately how long, in hours, will it take them to fill 1 truck?

A. 0.15
B. 0.31
C. 2.47
D. 3.23
E. 3.25

The OA is D.

First worker rate will be, 1/6 truck per hour.

Second worker rate will be, 1/7 truck per hour.

Then, their combined rates if they working together will be, 1/T = 1/6+1/7. Then T = (6*7)/(6+7) = 42/13 = 3.23 hours.

Is there a strategic approach to this PS question? Can any experts help, please? Thanks!

Well, if it were the case that we had two people, each of whom could perform a task individually in 6 hours, we know that if they worked together, they'd do the job in half the time, or in 3 hours. So because one of the individuals does the job in 7 hours, the answer has to be a little more than 3, leaving us with just D or E.

(My sense is that the GMAT would probably have been a little more artful about its answer choices, allowing you to use logic to determine which was correct without requiring much arithmetic.)

Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course

Like this post

GMAT/MBA Expert

Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Tue Feb 20, 2018 4:15 pm

AAPL wrote:A worker can load 1 full truck in 6 hours. A second worker can load the same truck in 7 hours. If both workers load one truck simultaneously while maintaining their constant rates, approximately how long, in hours, will it take them to fill 1 truck?

A. 0.15
B. 0.31
C. 2.47
D. 3.23
E. 3.25

One approach is to assign a nice value to the entire job (of filling a truck)

We want a number that works well with the given times (6 hours and 7 hours)
42 is such a number.
So, let's say that filling the truck is equivalent to shoveling 42 scoops of dirt into it.

A worker (we'll call worker A) can load 1 full truck in 6 hours
Rate = output/time = 42 scoops/6 hours = 7 scoops/hour
So, worker A's RATE is 7 scoops/hour

Worker B) can load 1 full truck in 7 hours
Rate = output/time = 42 scoops/7 hours = 6 scoops/hour
So, worker B's RATE is 6 scoops/hour

So, their COMBINED rate = 7 scoops/hour + 6 scoops/hour
= 13 scoops/hour

Worker B) Approximately how long, in hours, will it take them to fill 1 truck?
Time = output/rate
= 42 scoops/13 scoops/hour
= 42/13 hours
= 3 3/13 hours

ASIDE: Notice that 3 3/12 hours = 3.25 hours
So, 3 3/13 hours will equal a little less than 3.25 hours

Answer: D

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

Like this post

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10392; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Tue Feb 20, 2018 6:57 pm

Hi AAPL,

We're told that A worker can load 1 full truck in 6 hours, a second worker can load the same truck in 7 hours and both workers load one truck simultaneously while maintaining their constant rates. We're asked for the approximate amount of time, in hours, that it will take them to fill 1 truck. This is an example of a standard 'Work Formula' question.

Work = (A)(B)/(A+B) where A and B are the individual times it takes the two entities to complete the task on their own.

Here, the two values would be 6 and 7...

(6)(7)/(6+7) = 42/13 = 3 3/13 hours

Since 3/13 is LESS then 3/12 = 1/4, the correct answer has to be a little less than 3 1/4 hours

Final Answer: D

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

Like this post

Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Thu Feb 22, 2018 8:34 am

AAPL wrote:A worker can load 1 full truck in 6 hours. A second worker can load the same truck in 7 hours. If both workers load one truck simultaneously while maintaining their constant rates, approximately how long, in hours, will it take them to fill 1 truck?

A. 0.15
B. 0.31
C. 2.47
D. 3.23
E. 3.25

The combined rate of the two workers is 1/7 + 1/6 = 6/42 + 7/42 = 13/42.

Since time is inverse of rate, it will take 42/13 = 3 3/13 = 3.23 hours.

Answer: D

Jeffrey Miller
Head of GMAT Instruction
[email protected]

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review