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2 men and 3 boys can do a piece of work in 10 days while 3 men and 2

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Joined: 09 Jan 2016
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GPA: 3.4
WE: General Management (Human Resources)
2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 06:20
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2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days . In how many days can 2 man and 1 boy do the work?

A. 15
B. 18
C. 12.5
D. 10
E. 16
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Aug 2009
Posts: 5715
Re: 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 09:53
Expert's post
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Chemerical71 wrote:
2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days . In how many days can 2 man and 1 boy do the work?

A. 15
B. 18
C. 12.5
D. 10
E. 16

Two points before coming to the solution..
1) under no circumstances, it is sub-600 level.
2) the choices are always in ascending order, so may not be a very authentic source although the Q is ok.

Let m men can complete the job on their own and B boys can complete the work.
So $$\frac{2}{m}+\frac{3}{b}=\frac{1}{10}$$..
$$\frac{2*3}{m}+\frac{3*3}{b}=\frac{3}{10}$$..(i)

$$\frac{3}{m}+\frac{2}{b}=\frac{1}{8}$$...
$$\frac{2*3}{m}+\frac{2*2}{b}=\frac{2}{8}$$...(ii)

Subtract i from ii..
$$\frac{9}{b}-\frac{4}{b}=\frac{3}{10}-\frac{2}{8}$$..
$$\frac{5}{b}=\frac{1}{20}$$...
Or b=20*5=100..
Substitute in i to get value of m..
$$\frac{2}{m}+\frac{3}{100}=\frac{1}{10}$$..
$$\frac{2}{m}=\frac{1}{10}-\frac{3}{100}$$..
$$\frac{2}{m}=\frac{7}{100}$$..

We are looking for $$\frac{2}{m}+\frac{1}{b}=7/100+1/100=8/100$$..
So time taken=100/8=12.5..
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Re: 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 12:45
Let x be men and y boys
(2y+3x)/xy=1/10
(3y+2x)/xy=1/8
Through elimination you will get
X=2/7y
Therefore 10/y=1/10
Y rate=1/100
X rate=3.5/100
So rate of 2x+y=8/100 or 1/12.5 per day. Therefore it will be completed in 12.5 day

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2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 14:10
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2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days . In how many days can 2 man and 1 boy do the work?

A. 15
B. 18
C. 12.5
D. 10
E. 16

let m and b=rates for 1 man and 1 boy respectively
multiplying,
6m+9b=3/10 and
6m+4b=1/4
subtracting,
b=1/100
m=3.5/100
let d=days
d(7/100+1/100)=1
d=12.5 days
C
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Joined: 04 Jan 2015
Posts: 865
Re: 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 21:49
1
KUDOS
Expert's post
Chemerical71 wrote:
2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days . In how many days can 2 man and 1 boy do the work?

A. 15
B. 18
C. 12.5
D. 10
E. 16

• 2 men and 3 boys can do a piece of work in 10 days.
o Thus, 20 men and 30 boys can do a piece of work in 1 day......(i)

• 3 men and 2 boys can do the same work in 8 days.
o Thus, 24 men and 16 boys can do the same work in 1 day....(ii)

• Equating (i) and (ii) we get -
o 20 men + 30 boys = 24 men + 16 boys
o 4 men = 14 boys
o 2 men = 7 boys

• Substituting this in equation (i) we get

o 10 boys can do a piece of work in 10 days.
o But we need to find out in how many days 2 men and 1 boy can do the work, which is equivalent to 8 boys.

 8 boys can do the same work in (10*10/8) = 12.5 days.

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Saquib
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Manager
Joined: 09 Jan 2016
Posts: 130
GPA: 3.4
WE: General Management (Human Resources)
Re: 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 [#permalink]

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16 Apr 2017, 23:58
chetan2u wrote:
Chemerical71 wrote:
2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days . In how many days can 2 man and 1 boy do the work?

A. 15
B. 18
C. 12.5
D. 10
E. 16

Two points before coming to the solution..
1) under no circumstances, it is sub-600 level.
2) the choices are always in ascending order, so may not be a very authentic source although the Q is ok.

Let m men can complete the job on their own and B boys can complete the work.
So $$\frac{2}{m}+\frac{3}{b}=\frac{1}{10}$$..
$$\frac{2*3}{m}+\frac{3*3}{b}=\frac{3}{10}$$..(i)

$$\frac{3}{m}+\frac{2}{b}=\frac{1}{8}$$...
$$\frac{2*3}{m}+\frac{2*2}{b}=\frac{2}{8}$$...(ii)

Subtract i from ii..
$$\frac{9}{b}-\frac{4}{b}=\frac{3}{10}-\frac{2}{8}$$..
$$\frac{5}{b}=\frac{1}{20}$$...
Or b=20*5=100..
Substitute in i to get value of m..
$$\frac{2}{m}+\frac{3}{100}=\frac{1}{10}$$..
$$\frac{2}{m}=\frac{1}{10}-\frac{3}{100}$$..
$$\frac{2}{m}=\frac{7}{100}$$..

We are looking for $$\frac{2}{m}+\frac{1}{b}=7/100+1/100=8/100$$..
So time taken=100/8=12.5..
thank you for reply..I have been preparing for gmat since few months.For quant, i am doing manhattan, veritas and some gmat club solution mainly you , Bunnel after completing official sources.. I think this problem is consistent with gmat quant that's why i have posted.
Re: 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2   [#permalink] 16 Apr 2017, 23:58
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