Work Problem

Expert replies

talaangoshtari: Master | Next Rank: 500 Posts; Posts: 154; Joined: Wed May 21, 2014 4:29 amFollowed by: 1 member; Thanked: 8 times

by talaangoshtari » Mon Apr 04, 2016 4:13 am

The constant rate at which machines A works is 3/4 of the constant rate at which machine B works. Under normal conditions, machine A would complete x lots in 2 days. However, when a technician attempts to use machines A and B simultaneously, there is not enough electrical power to run both machines at full power. As a result, running the machines simultaneously reduces the work rate of each machine by 20%.

How long will it take the machines to complete 3x lots, working simultaneously?

Source: Beat The GMAT — Quantitative Reasoning | Mon Apr 04, 2016 4:13 am

MartyMurray: Legendary Member; Posts: 2135; Joined: Mon Feb 03, 2014 9:26 amFollowed by: 140 members; Location: https://martymurraycoaching.com/; Thanked: 955 times; GMAT Score:800

by MartyMurray » Mon Apr 04, 2016 5:02 am

One great, pretty much fail safe way to handle work problems is to start by finding the rates of each machine or person doing the work.

A Normal Rate: x/2 per day

B Normal Rate: (x/2)/(3/4) = 2x/3 per day

Rate Together: A Rate + B Rate = 3x/6 + 4x/6 = 7x/6 Per Day

Together Running At Reduced Rate: 7x/6 x 4/5 = 28x/30 = 14x/15

3x/(14x/15) = 3/(14/15) = 45/14 Days Working Simultaneously

Last edited by MartyMurray on Tue Apr 05, 2016 11:35 am, edited 1 time in total.

Marty Murray
Perfect Scoring Tutor With Over a Decade of Experience
MartyMurrayCoaching.com
Contact me at [email protected] for a free consultation.

GMAT/MBA Expert

[email protected]: Elite Legendary Member; Posts: 10391; Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members; Location: Palo Alto, CA; Thanked: 2867 times; GMAT Score:800

by [email protected] » Mon Apr 04, 2016 9:06 am

Hi talaangoshtari,

When posting GMAT questions, you should make sure to post the 5 answer choices as well. In many cases, the answers provide 'clues' as to how you can approach the question. Without having that option, we're essentially forced to 'do math' (as Marty has shown), although you could also TEST VALUES (choose a value for X and then calculate from there).

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

Contact Rich at [email protected]

talaangoshtari: Master | Next Rank: 500 Posts; Posts: 154; Joined: Wed May 21, 2014 4:29 amFollowed by: 1 member; Thanked: 8 times

by talaangoshtari » Mon Apr 04, 2016 11:01 am

Hi.
I know that. But, this is a GRE question. In GRE we have some questions without the answer choices.

regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

by regor60 » Tue Apr 05, 2016 10:55 am

Marty Murray wrote:One great, pretty much fail safe way to handle work problems is to start by finding the rates of each machine or person doing the work.

A Normal Rate: x/2 per day

B Normal Rate: (x/2)/(3/4) = 2x/3 per day

Rate Together: A Rate + B Rate = 3x/6 + 4x/6 = 7x/6 Per Day

Together Running At Reduced Rate: 7x/6 x 3x/4 = 21x/24 = 7x/8

3x/(7x/8) = 3/(7/8) = 24/7 Days Working Simultaneously

Question indicates 20% reduction not 25%. Would think T is 45/14

MartyMurray: Legendary Member; Posts: 2135; Joined: Mon Feb 03, 2014 9:26 amFollowed by: 140 members; Location: https://martymurraycoaching.com/; Thanked: 955 times; GMAT Score:800

by MartyMurray » Tue Apr 05, 2016 11:32 am

regor60 wrote:Question indicates 20% reduction not 25%. Would think T is 45/14

Yup. Fixed.

Marty Murray
Perfect Scoring Tutor With Over a Decade of Experience
MartyMurrayCoaching.com
Contact me at [email protected] for a free consultation.

Matt@VeritasPrep: GMAT Instructor; Posts: 2629; Joined: Wed Sep 12, 2012 3:32 pmFollowed by: 119 members; Location: East Bay all the way; Thanked: 625 times; GMAT Score:780

by Matt@VeritasPrep » Fri Apr 15, 2016 1:40 pm

Another popular approach is picking a value. Suppose x = 60. Then

A does 30 lots a day
B does 40 lots a day

after the power reduction,

A does 24 lots a day
B does 32 lots a day

So we've got 56 lots a day with the two together, and 180 lots for them to do.

180/56 => 4*45 / 4*15 => 45/14

Save $100 on any VP online course!

Featured schoolRound 2 closes Jan 7, 2027 54 days left

Chicago Booth

Since 1982, 10 Booth faculty members have received the Nobel Prize in Economic Sciences, more than any other business school.

#3
U.S. News rank: $175,000
Median base salary: 670
Average GMAT Focus: 635
Students in the class

Apply to Booth Visit chicagobooth.edu See the full profile

Photo: Warren LeMay, CC BY-SA 2.0

GMAT Course Reviews

563 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (563 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