Three machines, a, b, c, individually can do a certain job.

Question

Three machines, a, b, c, individually can do a certain job. What is the greatest part of that job that can be done in one hour by two of the machines working together at their respective rates?

(1) Machine a can complete the job in 5 hours.
(2) Machine b can complete the job in 7 hours.

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ManifestDreamMBA · Answer

To ascertain the greatest part of that job that can be done in one hour by two of the machines working together at their respective rates, we need the rate of work of all 3 to pick the fastest 2

S1
a = 5hrs
No info on b and c
insufficient

S2
b = 7hrs
No info on a and c
insufficient

Combined, we have info on a and b only and not c.
If c is the fastest or faster than b, the greatest part of the job will need to be carried out by c with a(faster of a and b).
If c is slowest, the greatest part of the job will need to be carried out by a and b.
Insufficient

Answer E

ravi1522 · Answer

Hello,
Three machines, a, b, c, individually can do a certain job. What is the greatest part of that job that can be done in one hour by two of the machines working together at their respective rates?

Statement 1 gives me the the rate A but still nothing about other two
Not sufficient

Statement 2 gives me that rate of B but still nothing about other two

Not sufficient

even when we combine we don"t know anything about the member c is he fast or slow or same

Hence Option E is correct

Thanks

akshatj28 · Answer

Question Stem: Three machines, a, b, c, individually can do a certain job. What is the greatest part of that job that can be done in one hour by two of the machines working together at their respective rates?

So, to answer this, I must be either able to get individual speed of a, b and c or some information that give me speed of any of these 3 ( a+b, b+c, c+a) and I would be able to answer my question.

In the Options:

Statement 1: It only gives me info about Machine A, and I don't know anything about B and C speed

Statement 2 : It only gives me info about Machine B, and I don't know anything about A and C speed

So, Option E - together not sufficient is the right choice.

Dereno · Answer

Three machines a b c can do a certain job.

Need to find the greatest job that can be completed in 1 hour, provided only 2 work on it.

So, we need the values of all three, at least two machines and the total hours taken or the rates of individual machines to arrive at a conclusive answer.

Question stem has not provided any key information about the machine jobs.

Statement 1:

(1) Machine a can complete the job in 5 hours.

The value of machine a = 5, but we don’t have any data on values of b,c or total time. Hence,  Insufficient

Statement 2:

(2) Machine b can complete the job in 7 hours.

The value of machine b = 7, but we don’t have any data on values of a,c or total time. Hence,  Insufficient

Combining both statements,

we get , a =5, b= 7. But, still the value of C or total time T is not given. So we cannot conclude or compare the max work done in one hour.

Hence,  option E

Aboyhasnoname · Answer

This is pretty straightforward....

We don't know the rate of C.

C can do the Job in 0.00000000000000001 hours 
or may be 1000000 hours...

So the greatest part will be by the fastest two machines depending on their rate

We don't know if c is in the fastest two 
Even if we know that, we don't know their rate.

So... E

Three machines, a, b, c, individually can do a certain job.

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GMAT Data Sufficiency (DS) Questions

Three machines, a, b, c, individually can do a certain job.

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