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A type A machine can complete a job in 5 hours and a type B [#permalink]
01 Dec 2005, 05:40

00:00

A

B

C

D

E

Difficulty:

35% (medium)

Question Stats:

73% (02:13) correct
27% (00:46) wrong based on 40 sessions

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?

Re: A type A machine can complete a job in 5 hours and a type B [#permalink]
01 Dec 2005, 07:40

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."

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

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

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

Answer D should be correct.

gmatclubot

Re: A type A machine can complete a job in 5 hours and a type B
[#permalink]
26 Sep 2014, 11:50