number of machines

[Deepthi Subbu]

12 identical machines , running continuously at the same constant rate, take 8 days to complete a shipment . How many additional machines , each running at the same constant rate , would be needed to reduce the time required to complete a shipment by 2 days?


Here what does the bold part mean??

[Laura GMAT Tutor]

To answer your question, "reduce the time needed by 2 days" means, it used to take 8 days, right? We need to reduce that time by 2 days. So instead of 8 days, it's 2 days fewer, so it's 6 days.

So the question means, "How many additional machines would you need to add so that it would take 6 days instead of 8?"

Give it another try now that you understand the question better (I hope)

[Laura GMAT Tutor]

I do questions like this in a weird way but it makes sense to me so I'll tell you about it.

I think of it as if there are 96 things that need to get shipped. (I chose 96 because it's 12x8.) For 12 machines to ship all 96 in 8 days, that means each machine can ship one thing per day for each of the 8 days.

What if you wanted to ship all 96 things in 6 days? 96/6 = 16. You'd have to pack 16 things per day. Well, these machines ship one thing per day. So to pack 16 things per day, you'd need 16 machines.

[spoiler]So you'd need 16 machines instead of 12, so you'd need 4 more machines.
[/spoiler]
I know that's kind of a weird way to do it but it always works for me so maybe some of you will like it too!

[jaymw]

12 machines need 8 days to do a certain amount of work.

The bold statement asks:

12+how many machines need 8-2=6 days to do the same amount of work?

That's a simple rule of three question.

If 12 machines need 8 days, then 48 machines will be 4 times as quick (hence, they need 2 days). 6 days is three times 2 days, so to do the job in 6 days you only need 1/3 of 48 machines = 16 machines.

If you have 16 machines (that means 16-12=4 additional machines) instead of the initial 12, you can reduce the time it takes to complete a shipment by 2 days.

Hope that was helpful.

[beat_gmat_09]

Proportion can also be applied.
No. of machines is indirect proportion to number of days required.
12 indirect 1/8
12=k/8
k=12*8
To reduce days to 6.
12+x = k/6
put k=12*8
x = 12*8/6 - 12
x = 4 machines.

[Deepthi Subbu]

Thanks Laura , that was definitely helpful and you got the right answer too . One biggest hurdle that I face is understanding the meaning of the question . And the case here was the same too . I somehow understood it the other way and was calculating to find the no of machines needed to finish the work off in 2 days

I know its an ugly mistake but how do I rectify??

@jaymw - Good shortcut , but my problem lies with understanding the question

[Laura GMAT Tutor]

Well, to be honest, the trick isn't really a trick... It's just English fluency. I'd suggest that you spend some time improving your understanding of higher level English. You may want to look into a Business or Academic English course near you -- there may be a low cost course that could improve your English fluency. It would be a good thing for you anyway! A lot of people are fluent in every day life situations but when it comes to the small details of Academic English, the kind tested on the GMAT -- that's different. I can only imagine how tough it would be to take this exam in a language that you're not 100% sure of. I wish I could offer you a quick fix solution.... but sometimes there isn't one.

[Deepthi Subbu]

Well, to be honest, the trick isn't really a trick... It's just English fluency. I'd suggest that you spend some time improving your understanding of higher level English. You may want to look into a Business or Academic English course near you -- there may be a low cost course that could improve your English fluency. It would be a good thing for you anyway! A lot of people are fluent in every day life situations but when it comes to the small details of Academic English, the kind tested on the GMAT -- that's different. I can only imagine how tough it would be to take this exam in a language that you're not 100% sure of. I wish I could offer you a quick fix solution.... but sometimes there isn't one.

Il try that out . Thanks Laura.