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# A contractor undertakes to do a job within 20 days and hires 60

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Manager
Joined: 13 Jun 2012
Posts: 199
Location: United States
WE: Supply Chain Management (Computer Hardware)
A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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02 Jan 2018, 15:23
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Difficulty:

55% (hard)

Question Stats:

66% (02:25) correct 34% (02:50) wrong based on 59 sessions

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A contractor undertakes to do a job within 20 days and hires 60 people to do it. After 5 days, he realizes that one fifth of the work is done so he hires more people. How many more man he has to hire to complete the job in time?

1. 10
2. 12
3. 15
4. 20
5. 25
Manager
Joined: 13 Jun 2012
Posts: 199
Location: United States
WE: Supply Chain Management (Computer Hardware)
A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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Updated on: 02 Jan 2018, 17:41

60 men *20 days= Total number of work 1200
Now after 5 days the amount of work that should be done was 5*60=300 but one fifth of the work was done ie 1200*1/5= 240
which means he still has= 960 amount of work
Let X be the number of men, So (60+x)15=960.. which is 4.

Originally posted by Turkish on 02 Jan 2018, 15:31.
Last edited by Turkish on 02 Jan 2018, 17:41, edited 1 time in total.
Manager
Joined: 20 Feb 2017
Posts: 88
Location: United States
Re: A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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02 Jan 2018, 16:36
1
Turkish wrote:
What am I doing wrong

60 men *20 days= Total number of work 1200
Now after 5 days the amount of work that should be done was 5*60=300 but one fifth of the work was done ie 1200*1/5= 240
which means he still has= 960 amount of work
Let X be the number of men, So (60+x)15=960.. which is 4.

You are missing that initial estimation of contractor was wrong.

60 people were able to complete only 1/5 of work in 5 days. So For person, it is 1500 days work not 1200.

Hope it helps.

Sent from my SM-G955F using GMAT Club Forum mobile app
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Joined: 07 Dec 2014
Posts: 1223
A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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02 Jan 2018, 19:23
Turkish wrote:
A contractor undertakes to do a job within 20 days and hires 60 people to do it. After 5 days, he realizes that one fifth of the work is done so he hires more people. How many more man he has to hire to complete the job in time?

1. 10
2. 12
3. 15
4. 20
5. 25

let 1/x=rate of one man for one day
60*1/x*5 days=1/5 of work
x=1500 days
let y=total men needed to finish job on time
y*1/1500*15 days=4/5 of work
y=80 men
80-60=20 more men needed
D
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 9695
Location: Pune, India
Re: A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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02 Jan 2018, 23:02
1
3
Turkish wrote:

60 men *20 days= Total number of work 1200
Now after 5 days the amount of work that should be done was 5*60=300 but one fifth of the work was done ie 1200*1/5= 240
which means he still has= 960 amount of work
Let X be the number of men, So (60+x)15=960.. which is 4.

Here is the problem - total amount of work to be done is not 1200.
60 people in 5 days did 60*5 = 300 man days work which is 1/5th of total work. So total work is actually 300*5 = 1500 man days.

So he has to do 1500 - 300 = 1200 man days of work in 15 days.
HE needs 1200/15 = 80 men to do it i.e. 20 more.
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Re: A contractor undertakes to do a job within 20 days and hires 60  [#permalink]

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03 May 2019, 06:20
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: A contractor undertakes to do a job within 20 days and hires 60   [#permalink] 03 May 2019, 06:20
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