Rates

Expert replies

artstudent: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Mar 28, 2011 9:35 pm; Thanked: 4 times

by artstudent » Wed Jul 20, 2011 9:37 pm

Crew A can build a car in 20 minutes and Crew B can build a car in 25 minutes. If both crews work independently and start at the same time, what is the least amount of time required for the two crews to build 10 complete cars?

I had 111(1/9) minutes. OA is 120. Can someone explain?

Like this post

Source: Beat The GMAT — Problem Solving | Wed Jul 20, 2011 9:37 pm

pemdas: Legendary Member; Posts: 1084; Joined: Fri Apr 15, 2011 2:33 pmFollowed by: 21 members; Thanked: 158 times

by pemdas » Wed Jul 20, 2011 10:40 pm

Crew A's speed 1/20
Crew B's speed 1/25
10 cars will be built in time T
>>>
1/20 - 1/25 = (5-4)/100 = 1/100 is the difference in speed between the crews A and B
hence 1 more (additional) car can be built by crew A than by crew B within 100 minutes

during first 100 minutes 5 cars can be built by crew A and 4 cars can be built by crew B + (Plus) within the next 20 minutes additional 1 (one car) can be built (completed by crew B. This makes T=100+20 or 120 minutes.

artstudent wrote:Crew A can build a car in 20 minutes and Crew B can build a car in 25 minutes. If both crews work independently and start at the same time, what is the least amount of time required for the two crews to build 10 complete cars?

I had 111(1/9) minutes. OA is 120. Can someone explain?

Success doesn't come overnight!

Like this post

winniethepooh: Master | Next Rank: 500 Posts; Posts: 370; Joined: Sat Jun 11, 2011 8:50 pmFollowed by: 2 members; Location: Arlington, MA.; Thanked: 27 times

by winniethepooh » Wed Jul 20, 2011 10:43 pm

As the work is done independently the combined work cannot be a fraction.

Consider first 100 hours of combined work:
Crew A makes 100/20 = 5 cars and Crew B makes 100/25 = 4 cars
Now 1 car has to be made so to take the least possible time and also prudently the car will be made by Crew A. Hence, additional 20 mins will be taken.
So, total = 100 + 20 mins = 120 mins.

Like this post

amit2k9: Master | Next Rank: 500 Posts; Posts: 461; Joined: Tue May 10, 2011 9:09 amFollowed by: 3 members; Location: pune; Thanked: 36 times

by amit2k9 » Thu Jul 21, 2011 1:39 am

In 100 mints A makes 5 and B makes 4 cars.
total = 9 cars made in 100 mints.

A takes less time to make 1 car = 20 min
hence 10th car will be made by A in 20 more mints.
total = 100+20 = 120 min

For Understanding Sustainability,Green Businesses and Social Entrepreneurship visit -https://aamthoughts.blocked/
(Featured Best Green Site Worldwide-https://bloggers.com/green/popular/page2)

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Thu Jul 21, 2011 2:32 am

artstudent wrote:Crew A can build a car in 20 minutes and Crew B can build a car in 25 minutes. If both crews work independently and start at the same time, what is the least amount of time required for the two crews to build 10 complete cars?

I had 111(1/9) minutes. OA is 120. Can someone explain?

We could plug in the answers, which the GMAT would provide.
One answer likely would say 100 minutes.
In 100 minutes, A produces 100/20 = 5 cars and B produces 100/25 = 4 cars.
Total cars produced in 100 minutes = 5+4 = 9 cars.
The faster crew -- A -- will require 20 more minutes to produce the 10th car.
Total time = 100+20 = 120 minutes.

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 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