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 hours will it take them to complete the project if they are working together?
$$\text{A. } \frac{xy}{x+y}$$
$$\text{B. } \frac{x+y}{xy}$$
$$\text{C. }x+y$$
$$\text{D. } xy$$
$$\text{E. }x-y$$
OA A.
If it takes Jacob x hours to complete a project and it
This topic has expert replies
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
For work questions, there are two useful rules:AAPL wrote: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 hours will it take them to complete the project if they are working together?
$$\text{A. } \frac{xy}{x+y}$$
$$\text{B. } \frac{x+y}{xy}$$
$$\text{C. }x+y$$
$$\text{D. } xy$$
$$\text{E. }x-y$$
OA A.
Rule #1: If a person can complete an entire job in k hours, then in one hour, the person can complete 1/k of the job
Example: If it takes Sue 5 hours to complete a job, then in one hour, she can complete 1/5 of the job. In other words, her work rate is 1/5 of the job per hour
Rule #2: If a person completes a/b of the job in one hour, then it will take b/a hours to complete the entire job
Example: If Sam can complete 1/8 of the job in one hour, then it will take him 8/1 hours to complete the job.
Likewise, if Joe can complete 2/3 of the job in one hour, then it will take him 3/2 hours to complete the job.
Let's use these rules to solve the question. . . .
It takes Jacob x hours to complete a project and it takes Mike y hours to complete the same project
So, applying Rule #1....
Jacob completes 1/x of the job in ONE HOUR
Mike completes 1/y of the job in ONE HOUR
So, in ONE HOUR, the two workers complete 1/x + 1/y of the job
1/x + 1/y = y/xy + x/xy
= (x + y)/xy
In other words, in ONE HOUR, the two workers complete (x + y)/xy of the job
Applying Rule #2, the total time to COMPLETE the job = xy/(x + y)
Answer: A
Cheers,
Brent
GMAT/MBA Expert
- Jeff@TargetTestPrep
- GMAT Instructor
- Posts: 1462
- Joined: Thu Apr 09, 2015 9:34 am
- Location: New York, NY
- Thanked: 39 times
- Followed by:22 members
Jacob's rate is 1/x, and Mike's rate is 1/y. We can create the following combined rate expression:AAPL wrote: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 hours will it take them to complete the project if they are working together?
$$\text{A. } \frac{xy}{x+y}$$
$$\text{B. } \frac{x+y}{xy}$$
$$\text{C. }x+y$$
$$\text{D. } xy$$
$$\text{E. }x-y$$
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
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
- fskilnik@GMATH
- GMAT Instructor
- Posts: 1449
- Joined: Sat Oct 09, 2010 2:16 pm
- Thanked: 59 times
- Followed by:33 members
Let´s use UNITS CONTROL, one of the most powerful tools of our method!AAPL wrote: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 hours will it take them to complete the project if they are working together?
\[\text{A. } \frac{xy}{x+y} \,\,\,\,\, \text{B. } \frac{x+y}{xy} \,\,\,\,\, \text{C. }x+y \,\,\,\,\, \text{D. } xy \,\,\,\,\, \text{E. }x-y \]
\[J\,\,:\,\,\,\frac{{x\,\,\,{\text{h}}}}{{1\,\,{\text{job}}}}\,\,\, \to \,\,\,\frac{1}{x}\,\,\,\frac{{{\text{job}}}}{{\text{h}}}\,\,\,\,\,\,\,\,;\,\,\,\,\,\,M:\,\,\frac{{y\,\,{\text{h}}}}{{1\,\,{\text{job}}}}\,\,\,\, \to \,\,\,\frac{1}{y}\,\,\,\frac{{{\text{job}}}}{{\text{h}}}\]
\[?\,\,\,:\,\,{T_{\,J\, \cup \,M}}\,\,\,\,\left( {1\,\,\,{\text{job}}} \right)\]
\[J \cup M\,\,:\,\,\,\,\,\,{T_{\,J\, \cup \,M}}\,\,{\text{h}}\,\, \cdot \left( {\frac{1}{x} + \frac{1}{y}} \right)\,\,\frac{{{\text{job}}}}{{\text{h}}}\,\,\, = \,\,\,1\,\,\,{\text{job}}\]
\[{T_{\,J\, \cup \,M}}\left( {\frac{{y + x}}{{xy}}} \right)\,\,\, = \,\,\,1\,\,\,\,\,\,\,\,\, \Rightarrow \,\,\,\,\,\,\,? = \frac{{xy}}{{x + y}}\,\,\]
The above follows the notations and rationale taught in the GMATH method.
Regards,
fskilnik.
Fabio Skilnik :: GMATH method creator ( Math for the GMAT)
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br
English-speakers :: https://www.gmath.net
Portuguese-speakers :: https://www.gmath.com.br