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

 It is currently 13 Oct 2019, 21:05

### 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

# Three neighborhood children, individually, can mow Mr. Phelps's lawn i

Author Message
TAGS:

### Hide Tags

Manager
Joined: 13 Sep 2016
Posts: 115
GMAT 1: 800 Q51 V51
Three neighborhood children, individually, can mow Mr. Phelps's lawn i  [#permalink]

### Show Tags

16 Oct 2016, 02:38
00:00

Difficulty:

5% (low)

Question Stats:

91% (01:27) correct 9% (01:09) wrong based on 110 sessions

### HideShow timer Statistics

Three neighborhood children, individually, can mow Mr. Phelps's lawn in 1.5, 2, and 3 hours, respectively. What is the fastest the job can be completed by two of the children working together at their respective rates?

a) 6/7 hours
b) 3/2 hours
c) 7/4 hours
d) 7/2 hours
e) 5 hours

Math Expert
Joined: 02 Sep 2009
Posts: 58335
Re: Three neighborhood children, individually, can mow Mr. Phelps's lawn i  [#permalink]

### Show Tags

16 Oct 2016, 02:45
1
2
alanforde800Maximus wrote:
Three neighborhood children, individually, can mow Mr. Phelps's lawn in 1.5, 2, and 3 hours, respectively. What is the fastest the job can be completed by two of the children working together at their respective rates?

a) 6/7 hours
b) 3/2 hours
c) 7/4 hours
d) 7/2 hours
e) 5 hours

The fastest children are those who can mow the lawn in 1.5 (3/2) and 2 hours. Their individual rates are 2/3 and 1/2 lawn/hour.

Their combined rate is 2/3 + 1/2 = 7/6 lawn/hour. The time is a reciprocal of the rate, thus working together at their respective rates these two children can mow the lawn in 6/7 hours.

_________________
Board of Directors
Status: QA & VA Forum Moderator
Joined: 11 Jun 2011
Posts: 4753
Location: India
GPA: 3.5
Re: Three neighborhood children, individually, can mow Mr. Phelps's lawn i  [#permalink]

### Show Tags

16 Oct 2016, 03:34
1
alanforde800Maximus wrote:
Three neighborhood children, individually, can mow Mr. Phelps's lawn in 1.5, 2, and 3 hours, respectively. What is the fastest the job can be completed by two of the children working together at their respective rates?

a) 6/7 hours
b) 3/2 hours
c) 7/4 hours
d) 7/2 hours
e) 5 hours

Let the total work be 6 units...

Efficiency of child A = 6/1.5 = 4 units/hour
Efficiency of child B = 6/2 = 3 units/hour
Efficiency of child C = 6/3 = 2 units/hour

Quote:
What is the fastest the job can be completed by two of the children working together at their respective rates?

Since the efficiency of child A and Child B are faster than C , their combined efficiency is 7 ( ie, 4 + 3 )

So, Time taken by A and B working at their respective rates is 6/7

Hence correct answer must be (A)

_________________
Thanks and Regards

Abhishek....

PLEASE FOLLOW THE RULES FOR POSTING IN QA AND VA FORUM AND USE SEARCH FUNCTION BEFORE POSTING NEW QUESTIONS

How to use Search Function in GMAT Club | Rules for Posting in QA forum | Writing Mathematical Formulas |Rules for Posting in VA forum | Request Expert's Reply ( VA Forum Only )
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 15234
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: Three neighborhood children, individually, can mow Mr. Phelps's lawn i  [#permalink]

### Show Tags

26 Jan 2018, 13:33
Hi All,

You can answer this question with 10 seconds of logical thinking and no actual work - and you're not likely to see questions designed in that way on the Official GMAT.

Since the individual times it takes to mow the lawn are 1.5 hours, 2 hours and 3 hours, the fastest child can mow the lawn by himself in 1.5 hours. If he has help, then it would take LESS time than that - there's only one answer that logically fits...

GMAT assassins aren't born, they're made,
Rich
_________________
Contact Rich at: Rich.C@empowergmat.com

The Course Used By GMAT Club Moderators To Earn 750+

souvik101990 Score: 760 Q50 V42 ★★★★★
ENGRTOMBA2018 Score: 750 Q49 V44 ★★★★★
Re: Three neighborhood children, individually, can mow Mr. Phelps's lawn i   [#permalink] 26 Jan 2018, 13:33
Display posts from previous: Sort by