GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 22 Apr 2019, 23:12

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# 3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 7238
GMAT 1: 760 Q51 V42
GPA: 3.82
3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the  [#permalink]

### Show Tags

04 Jul 2017, 03:01
2
2
00:00

Difficulty:

15% (low)

Question Stats:

87% (01:35) correct 13% (01:22) wrong based on 68 sessions

### HideShow timer Statistics

3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the greatest part of the task that can be finished by two of these robots together in 1 hour?

$$A. \frac{13}{42} B. \frac{11}{42} C. \frac{42}{13} D. \frac{42}{11} E. \frac{13}{21}$$

_________________
MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Senior SC Moderator Joined: 22 May 2016 Posts: 2648 3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the [#permalink] ### Show Tags 04 Jul 2017, 03:30 2 MathRevolution wrote: 3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the greatest part of the task that can be finished by two of these robots together in 1 hour? $$A. \frac{13}{42} B. \frac{11}{42} C. \frac{42}{13} D. \frac{42}{11} E. \frac{13}{21}$$ Nice question. Rates of three robots respectively are $$\frac{1}{6}$$, $$\frac{1}{7}$$, and $$\frac{1}{8}$$. To maximize the greatest part of the work that gets done, we need the two fastest robots, i.e., those which take less time to do more work, and we need their combined rate. $$\frac{1}{6}$$ + $$\frac{1}{7}$$ = $$\frac{13}{42}$$. Greatest part of work that can be done by two fastest robots together in 1 hour? $$r*t = W$$ ---> $$\frac{13}{42}$$ * 1 = $$\frac{13}{42}$$. Answer A Trap answer is C. These question often ask for time. This one asks for work. _________________ Listen, are you breathing just a little, and calling it a life? -- Mary Oliver For practice SC questions with official explanations that were posted and moderated by the SC Team, go to SC Butler here: https://gmatclub.com/forum/project-sc-butler-get-2-sc-questions-everyday-281043.html Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 7238 GMAT 1: 760 Q51 V42 GPA: 3.82 Re: 3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the [#permalink] ### Show Tags 07 Jul 2017, 01:09 ==> Assuming that A, B, and C finishes their tasks in 6hrs, 7hrs, and 8 hrs each, the work rate of A and B are good, and each finished $$\frac{1}{6}$$ and $$\frac{1}{7}$$, so you get $$\frac{1}{6}+\frac{1}{7}=\frac{13}{42}$$. The answer is A. Answer: A _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"
Re: 3 robots can finish the same task in 6hrs, 7hrs, and 8hrs.What is the   [#permalink] 07 Jul 2017, 01:09
Display posts from previous: Sort by