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

Redeem

Work problem.

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 51
Joined: Sat Oct 16, 2010 9:31 pm

Work problem.

by AndyB » Sun Nov 07, 2010 8:18 am
Hi All,

Please help me in understanding the concept behind this quesiton.

Q)45 men can complete a work in 16 days.Six days after they started working, 25 more men joined them.How many days will they now take to complete the remaining work..???
Ans)6 days

Explanation-
M1xD1/W1=M2xD2/W2
45x6/(6/16)=75xdx(1-(6/16))
=6

I understand the calculation part, I have few questions.

1)What is this formula - M1xD1/Wi=M2xD2/W2..???
2)How come work done by 45 men in 6/16 days equal to the remaining work done by 75 men in 1-6/16 days...??(Seriously confused at this point)

I just dont want blindly to use the formula.
Top
Source: — Problem Solving |
Senior | Next Rank: 100 Posts
Posts: 70
Joined: Sun Jul 22, 2007 11:43 pm
Thanked: 8 times

by Bharat » Sun Nov 07, 2010 9:16 am
Answer 6 days (with a correction in the problem statement: 30 persons must have joined the team later rather than 25)
Approach:
45 Men > 1 Work > 16 days
1 Man > 1 Work > 16*45 days

Work completed by 45 men in 6 days = 6/16 work
remaining work after 6 days: 1 - (6/16) = 10/16 work
new work force: 45 + 30 = 75

75 Men > 10/16 work > (1 man's workdays/75)* (remaining work)
= (16*45/75)*(10/16) = 6 days

PS: if we calculate with addition of 25 men then answer is a fractional value: 45/7

Let me know in case of any questions. Thanks.
Top
Legendary Member
Posts: 1119
Joined: Fri May 07, 2010 8:50 am
Thanked: 29 times
Followed by:3 members

by diebeatsthegmat » Sun Nov 07, 2010 11:31 am
AndyB wrote:Hi All,

Please help me in understanding the concept behind this quesiton.

Q)45 men can complete a work in 16 days.Six days after they started working, 25 more men joined them.How many days will they now take to complete the remaining work..???
Ans)6 days

Explanation-
M1xD1/W1=M2xD2/W2
45x6/(6/16)=75xdx(1-(6/16))
=6

I understand the calculation part, I have few questions.

1)What is this formula - M1xD1/Wi=M2xD2/W2..???
2)How come work done by 45 men in 6/16 days equal to the remaining work done by 75 men in 1-6/16 days...??(Seriously confused at this point)

I just dont want blindly to use the formula.
heyyyy
how come it is 6 days while its only 25 more workers?
Top
User avatar
Legendary Member
Posts: 866
Joined: Mon Aug 02, 2010 6:46 pm
Location: Gwalior, India
Thanked: 31 times

by goyalsau » Sun Nov 07, 2010 1:07 pm
Bharat wrote:Answer 6 days (with a correction in the problem statement: 30 persons must have joined the team later rather than 25)
Approach:
45 Men > 1 Work > 16 days
1 Man > 1 Work > 16*45 days

Work completed by 45 men in 6 days = 6/16 work
remaining work after 6 days: 1 - (6/16) = 10/16 work
new work force: 45 + 30 = 75

75 Men > 10/16 work > (1 man's workdays/75)* (remaining work)
= (16*45/75)*(10/16) = 6 days

PS: if we calculate with addition of 25 men then answer is a fractional value: 45/7

Let me know in case of any questions. Thanks.
You are right it should be 30,
People just don't check , its really sad,
Saurabh Goyal
[email protected]
-------------------------


EveryBody Wants to Win But Nobody wants to prepare for Win.
Top
Senior | Next Rank: 100 Posts
Posts: 51
Joined: Sat Oct 16, 2010 9:31 pm

by AndyB » Sun Nov 07, 2010 7:02 pm
Hi All,

Its not 30 persons to be added, It is 25 persons.
Previously there was a typo, I have put the formula right but the calculation done by me was wrong.
Really soory for this.

Problem Explanation:

M1xD1/W1=M2xD2/W2
45x6/(6/16)=75xd/(1-(6/16))
(45 x6x16)/6=(75xdx16)/10
45x16=15x8xd
d=6

My concern is really what i have said in my post.
Top
User avatar
Legendary Member
Posts: 866
Joined: Mon Aug 02, 2010 6:46 pm
Location: Gwalior, India
Thanked: 31 times

by goyalsau » Sun Nov 07, 2010 7:46 pm
AndyB wrote:Hi All,

Its not 30 persons to be added, It is 25 persons.
Previously there was a typo, I have put the formula right but the calculation done by me was wrong.
Really soory for this.

Problem Explanation:

M1xD1/W1=M2xD2/W2
45x6/(6/16)=75xd/(1-(6/16)) ( 45+ 25 is not 75 , as i know )
(45 x6x16)/6=(75xdx16)/10
45x16=15x8xd
d=6

My concern is really what i have said in my post.
Dear i must say, you questions has really made me crazy, Sadly i was working on Work problems ,,, as i studied the concept just few days back, I was really worried how am i wrong..............

What to say, Guys,,,,,,,,
Saurabh Goyal
[email protected]
-------------------------


EveryBody Wants to Win But Nobody wants to prepare for Win.
Top
Senior | Next Rank: 100 Posts
Posts: 51
Joined: Sat Oct 16, 2010 9:31 pm

by AndyB » Sun Nov 07, 2010 9:09 pm
Sorry Guys,

U were correct, after working on this work rate problems.
Looks like I have gone out of my mind.
Yes it should me 30 persons.

But could anyone shed some light on the formula and how to use it.

Once again sorry guys for causing trouble.
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Mon Nov 08, 2010 4:00 am
AndyB wrote:Hi All,

Please help me in understanding the concept behind this quesiton.

Q)45 men can complete a work in 16 days.Six days after they started working, 30 more men joined them.How many days will they now take to complete the remaining work..???
Ans)6 days

Explanation-
M1xD1/W1=M2xD2/W2
45x6/(6/16)=75xdx(1-(6/16))
=6

I understand the calculation part, I have few questions.

1)What is this formula - M1xD1/Wi=M2xD2/W2..???
2)How come work done by 45 men in 6/16 days equal to the remaining work done by 75 men in 1-6/16 days...??(Seriously confused at this point)

I just dont want blindly to use the formula.
We could plug in a value for how much work is being done by each man.

Plug in that each man completes 2 unit/day.
Thus, 45 men complete 45*2 = 90 units/day.
Over 16 days, 16*90= 1440 units are completed. This is the value of the job.
In 6 days, 45 men complete 6*90 = 540 units.
1440-540 = 900 units left.
When 30 men join, total men = 45+30 = 75 men.
Rate for 75 men = 75*2 = 150/day.
Time for 75 men = w/r = 900/150 = 6 days.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Senior | Next Rank: 100 Posts
Posts: 51
Joined: Sat Oct 16, 2010 9:31 pm

by AndyB » Mon Nov 08, 2010 4:24 am
Thank You Mitch.
It was very simple but I struggled a lot to understand when i used the formula.
Top
Post new topic Post Reply
• Page 1 of 1