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

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

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New post 02 Jan 2018, 14:23
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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
[Reveal] Spoiler: OA

Kudos [?]: 114 [0], given: 341

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WE: Supply Chain Management (Computer Hardware)
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A contractor undertakes to do a job within 20 days and hires 60 [#permalink]

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New post 02 Jan 2018, 14:31
What am I doing wrong Can you please help? VeritasPrepKarishma

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.

Last edited by Turkish on 02 Jan 2018, 16:41, edited 1 time in total.

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Re: A contractor undertakes to do a job within 20 days and hires 60 [#permalink]

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New post 02 Jan 2018, 15:36
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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.

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

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New post 02 Jan 2018, 18:23
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

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Re: A contractor undertakes to do a job within 20 days and hires 60 [#permalink]

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New post 02 Jan 2018, 22:02
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Turkish wrote:
What am I doing wrong Can you please help? VeritasPrepKarishma

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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Kudos [?]: 18479 [1], given: 237

Re: A contractor undertakes to do a job within 20 days and hires 60   [#permalink] 02 Jan 2018, 22:02
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A contractor undertakes to do a job within 20 days and hires 60

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