If it takes Jacob x hours to complete a project and it

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BTGmoderatorLU: Moderator; Posts: 2505; Joined: Sun Oct 15, 2017 1:50 pm; Followed by:6 members

If it takes Jacob x hours to complete a project and it

by BTGmoderatorLU » Thu Dec 27, 2018 6:34 pm

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Source: Veritas Prep

If it takes Jacob x hours to complete a project and it takes Mike y hours to complete the same project, how many will it take them to complete the project if they are worling together?

A. xy/(x+y)
B. (x+y)/xy
C. x+y
D. xy
E. x-y

The OA is A

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Source: Beat The GMAT — Problem Solving | Thu Dec 27, 2018 6:34 pm

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

by [email protected] » Sat Dec 29, 2018 11:12 am

Hi All,

We're told that it takes Jacob X hours to complete a project and it takes Mike Y hours to complete the same project. We're asked for the number of hours it would take them to complete the project if they worked together. This is a great 'concept' question; if you recognize the concepts involved, you can actually answer it without doing any calculations.

When 2 entities (people, machines, etc.) work on a task together for the same amount of time, you can the Work Formula to determine how long it takes them to complete the task:

Work = (A)(B)/(A+B) where A and B are the two individual times it takes to complete the job

Here, we have two people working for the same amount of time, so we know that the Work Formula will apply. This gives us (X)(Y)/(X+Y).

Final Answer: A

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

Contact Rich at [email protected]

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Sun Feb 10, 2019 7:24 am

BTGmoderatorLU wrote:Source: Veritas Prep

If it takes Jacob x hours to complete a project and it takes Mike y hours to complete the same project, how many will it take them to complete the project if they are worling together?

A. xy/(x+y)
B. (x+y)/xy
C. x+y
D. xy
E. x-y

The OA is A

Jacob's rate is 1/x, and Mike's rate is 1/y. We can create the following combined rate expression:

1/x + 1/y = y/xy + x/xy = (x + y)/xy

Since time is the inverse of rate, it will take them xy/(x+y) hours to complete the project.

Answer: A

Scott Woodbury-Stewart
Founder and CEO
[email protected]