BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Please correct my reasoning on DS question

Problem Solving — algebra and arithmetic (GMAT Focus Edition)
Expert replies
by shoot4greatness » Fri Jan 28, 2011 4:41 pm
Three machines, K, M, and P, working simultaneously and independently at their respective constant rates, can complete a certain task in 24 minutes. How long does it take Machine K, working alone at its constant rate, to complete the task?

(1) Machines M and P, working simultaneously and independently at their respective constant rates, can complete the task in 36 minutes.

(2) Machines K and P, working simultaneously and independently at their respective constant rates, can complete the task in 48 minutes.

My reasoning:

From the question, you can set up an equation 1/k + 1/m + 1/p = 1/24
(1) From this data, we can set up an equation 1/m + 1/p = 1/24. Plug it into the equation from the quesiton and solve for k. Sufficient.

(2) From this data, you can set up an equation 1/k + 1/p = 1/48 Plug it into the equation, we can only find the value of m.
Join the discussion
Source: — Quantitative Reasoning |

by shoot4greatness » Fri Jan 28, 2011 4:43 pm
Continueing

Since the question deals with 3 different distinct variable, we need 3 different distint equations. From the question and the data, we only have 2. Insufficient.

Answer A
Join the discussion

by Tani » Sat Jan 29, 2011 1:58 pm
You don't need three equations because you are not solving for each of the three variables. Clue a gives you a value for M and P, the remainder will be K. You can't separate M and P with this clue, but you can isolate K.

From the second clue you can pull out K and P, leaving M. You cannot isolate K or P.

Try thinking of M and P as a single machine that can complete the work in 36 minutes. You then have two machines (MP and K) and two equations.
Tani Wolff
Join the discussion

by VivianKerr » Fri Feb 04, 2011 11:46 am
Here's my thinking:

- Value question - only a definitive number for the amount of time it takes Machine K alone will be sufficient.

- Given info: together the 3 machines complete in 24 min.

(1) Machines M + P together do it in 36 min. We can solve for K. SUFF.

(2) Machines K + P together do it in 48. Here, we do not know what of the 48 min. we can attribute to K, and what we can attribute to P. NOT SUFF.
Vivian Kerr
GMAT Rockstar, Tutor
https://www.GMATrockstar.com
https://www.yelp.com/biz/gmat-rockstar-los-angeles

Former Kaplan and Grockit instructor, freelance GMAT content creator, now offering affordable, effective, Skype-tutoring for the GMAT at $150/hr. Contact: [email protected]

Thank you for all the "thanks" and "follows"! :-)
Join the discussion