Machine \(A\) working alone can complete a job in \(3\frac12\) hours. Machine \(B\) working alone can do the same job in \(4\frac23\) hours. How long will it take both machines working together at their respective constant rates to complete the job?
A. 1hr 10 min
B. 2hr
C. 4hr 5 min
D. 7hr
E. 8hr 10 min
Answer: B
Source: Official Guide
5-Day Free Trial
5-day free, full-access trial TTP
Available with Beat the GMAT members only code
MORE DETAILS
Machine \(A\) working alone can complete a job in \(3\frac12\) hours. Machine \(B\) working alone can do the same job in
This topic has expert replies
-
Gmat_mission
- Legendary Member
- Posts: 1622
- Joined: Thu Mar 01, 2018 7:22 am
- Followed by:2 members
Timer
00:00
Your Answer
A
B
C
D
E
Global Stats
GMAT/MBA Expert
-
Scott@TargetTestPrep
- GMAT Instructor
- Posts: 7307
- Joined: Sat Apr 25, 2015 10:56 am
- Location: Los Angeles, CA
- Thanked: 43 times
- Followed by:29 members
Solution:Gmat_mission wrote: ↑Tue Nov 10, 2020 7:24 amMachine \(A\) working alone can complete a job in \(3\frac12\) hours. Machine \(B\) working alone can do the same job in \(4\frac23\) hours. How long will it take both machines working together at their respective constant rates to complete the job?
A. 1hr 10 min
B. 2hr
C. 4hr 5 min
D. 7hr
E. 8hr 10 min
Answer: B
Source: Official Guide
We see that Machine A’s rate is 1/(7/2) = 2/7 and Machine B’s rate = 1/(14/3) = 3/14. Therefore, their combined rate is 2/7 + 3/14 = 4/14 + 3/14 = 7/14 = 1/2. Since time is the inverse of rate, the time it will take both machines working together at their respective rates to complete the job is 1/(1/2) = 2 hours.
Answer: B
Scott Woodbury-Stewart
Founder and CEO
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews
