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# A type A machine can complete a job in 5 hours and a type B

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GMAT Club Legend
Joined: 29 Jan 2005
Posts: 4949
A type A machine can complete a job in 5 hours and a type B  [#permalink]

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Updated on: 01 Dec 2005, 08:09
4
00:00

Difficulty:

15% (low)

Question Stats:

77% (01:24) correct 23% (01:46) wrong based on 305 sessions

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A type A machine can complete a job in 5 hours and a type B machine can complete the job in 7 hours. How many hours will it take 2 type A machines and 3 type B machines working together and independently to complete the job?

A. 1/5
B. 29/35
C. 5/6
D. 35/29
E. 35/12

Originally posted by GMATT73 on 01 Dec 2005, 05:40.
Last edited by GMATT73 on 01 Dec 2005, 08:09, edited 1 time in total.
Director
Joined: 13 Nov 2003
Posts: 764
Location: BULGARIA
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 07:23
Can you, please elaborate on the meaning of" together and independently"
Thanx
GMAT Club Legend
Joined: 29 Jan 2005
Posts: 4949
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 07:40
1
BG wrote:
Can you, please elaborate on the meaning of" together and independently"
Thanx

I was also initially confused by such verbiage. However, this phrasing isn`t just Kaplish, it appears over and over again in various prep materials, so just accept it as "the machines/people/computers etc. work at their full capacity without complementing each other."

Hope that helps.
SVP
Joined: 28 May 2005
Posts: 1580
Location: Dhaka
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:10
Matt I am getting 10/7

A need 5 hours to complete

and B needs 10 hours to compete

so 2A + 3B will complete 2/5 + 3/10 or 7/10 portion of the job in 1 hour

so the whole job will take 10/7 hours....

am I missing something....
GMAT Club Legend
Joined: 29 Jan 2005
Posts: 4949
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:12
remgeo wrote:
I am also getting 10/7

2*1/5 + 3*1/10 = 10/7

Even with the edit, you are still missing a step.
SVP
Joined: 24 Sep 2005
Posts: 1782
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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Updated on: 01 Dec 2005, 08:16
hik, it kept me pondering for a while ...wonder what i missed here (without the edition)
Matt, take good rest after such a busy week!!

Originally posted by laxieqv on 01 Dec 2005, 08:13.
Last edited by laxieqv on 01 Dec 2005, 08:16, edited 1 time in total.
SVP
Joined: 28 May 2005
Posts: 1580
Location: Dhaka
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:16
1
1
now D should be the answer.

A need 5 hours to complete

and B needs 7 hours to compete

so 2A + 3B will complete 2/5 + 3/7 or 29/35 portion of the job in 1 hour

so the whole job will take 35/29 hours....
GMAT Club Legend
Joined: 29 Jan 2005
Posts: 4949
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:18
This is from the Kaplan White Course Book. The OE is a page long but makes no logical sense.
Director
Joined: 24 Oct 2005
Posts: 619
Location: London
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:21
GMATT73 wrote:
remgeo wrote:
I am also getting 10/7

2*1/5 + 3*1/10 = 10/7

Even with the edit, you are still missing a step.

2*1/5 + 3*1/7 = 29/35

Ans = 35/29

I still cant see what step I missed
GMAT Club Legend
Joined: 29 Jan 2005
Posts: 4949
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:33
remgeo wrote:
GMATT73 wrote:
remgeo wrote:
I am also getting 10/7

2*1/5 + 3*1/10 = 10/7

Even with the edit, you are still missing a step.

2*1/5 + 3*1/7 = 29/35

Ans = 35/29

I still cant see what step I missed

The step highlighted in red. When did you decide to include it?
Director
Joined: 24 Oct 2005
Posts: 619
Location: London
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 08:41
GMATT73 wrote:
remgeo wrote:
GMATT73 wrote:
remgeo wrote:
I am also getting 10/7

2*1/5 + 3*1/10 = 10/7

Even with the edit, you are still missing a step.

2*1/5 + 3*1/7 = 29/35

Ans = 35/29

I still cant see what step I missed

The step highlighted in red. When did you decide to include it?

Well, I had included that earlier as well.
10/7 was my conclusion
2/5 + 3/10 was the evidence
The assumption which is hidden was that I had taken the reverse of 7/10 to get the answer

Dont you think I need some rest !!
Senior Manager
Joined: 11 Nov 2005
Posts: 303
Location: London
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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01 Dec 2005, 09:22
Ans. D

My expl. A needs 5 hours to complete the job
2A need 5/2 hours to complete the job,

similarly 3B need 7/3 hours to complete the job

Lets consider 2A and 3B as single entity (X, Y)

so

1/X + 1/Y = 1/Z Z is the time to complete the job if working together.

1/(2/5) + 1/(7/3) =1/Z
2/5 + 3/7 =1/Z
29/35 = 1/Z

Z = 35/29

so if 2A and 3 B working together, they would need 35/29 hours to complete the job.

WORKING TOHETHER and INDEPENDENTLY means they work together without interfering each other hence they use their full potential to complete the job!

Does this sound sensible????

or simply.

1/5+1/5+1/7+1/7+1/7 =1/Z ( Z: time to work together)

Z = 35/29
Senior Manager
Joined: 11 May 2004
Posts: 427
Location: New York
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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02 Dec 2005, 13:01
Machine A's rate =1/5
Machine B's rate = 1/7

We have 2 A machines and 3 B machines = 1/5+1/5+1/7+1/7+1/7
Find the common denominator ie 35 and solve

You will get 29/35. This means that the machines can do 29/35 of the work in 1 hour. The question is asking how many hours does it take?

So, you take the inverse and you get 35/29.
Senior Manager
Joined: 03 Nov 2005
Posts: 319
Location: Chicago, IL
Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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02 Dec 2005, 15:48
Basic formula for the rate 1/a+1/b+1/c.....=1/Z time=Z

Rate for is A 1/5 and B works at the rate 1/7; 2A=2/5 and 3B=3/7

2/5+3/7=29/35 Flip it. 35/29. That Kaplish stuff can only appear at the beginning of Math section. Actual test questions appear to be much harder than that.
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GPA: 3.75
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Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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26 Sep 2014, 11:50
A type A machine can complete a job in 5 hours and a type B machine can complete the job in 7 hours. How many hours will it take 2 type A machines and 3 type B machines working together and independently to complete the job?

--just remember rate*time=job
Lets consider they both need to type for t hours to get the job done..

So, rate*time=job (Here job is 1 as it needs to be completed)
rate for type A machine =1/5 -- effective rate for 2 machines =2/5
similarly for type B machine effective rate for 2 machines =3/7

Finally we have,
(2/5)*t + (3/7)*t=1
t(29/35)=1
t=35/29

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Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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10 Oct 2016, 06:00
GMATT73 wrote:
A type A machine can complete a job in 5 hours and a type B machine can complete the job in 7 hours. How many hours will it take 2 type A machines and 3 type B machines working together and independently to complete the job?

A. 1/5
B. 29/35
C. 5/6
D. 35/29
E. 35/12

Let the total work be 35 ( LCM of 5 & 7 )

So, Efficiency of type A machines = 35/5 => 7
Efficiency of type A machines = 35/7 => 5

Quote:
How many hours will it take 2 type A machines and 3 type B machines working together

Combined efficiency will be -

Type A = 2*7 => 14
Type B = 3*5 => 15

Total efficiency is 14 + 15 = 29

So, Time taken will be 35/29

Hence correct answer will be (D) 35/29

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Re: A type A machine can complete a job in 5 hours and a type B  [#permalink]

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19 Oct 2018, 03:49
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Re: A type A machine can complete a job in 5 hours and a type B   [#permalink] 19 Oct 2018, 03:49
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