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gmatprep

by sq720 » Tue Nov 10, 2009 5:06 pm
Certain instruments used in veterinary surgery can be made either of stainless steel or of nylon. In a study of such instruments, 10 complete sterilizations of a set of nylon instruments required 3.4 times the amount of energy used to manufacture that set of instruments, whereas 50 complete sterilizations of a set of stainless steel instruments required 2.1 times the amount of energy required to manufacture that set of instruments.
If the statements above are true, each of the following could be true EXCEPT:
(A) The 50 complete sterilizations of nylon instruments used more energy than did the 50 complete sterilizations of the stainless steel instruments.
(B) More energy was required for each complete sterilization of the nylon instruments than was required to manufacture the nylon instruments.
(C) More nylon instruments than stainless steel instruments were sterilized in the study.
(D) More energy was used to produce the stainless steel instruments than was used to produce the nylon instruments.
(E) The total cost of 50 complete sterilizations of the stainless steel instruments was greater than the cost of manufacturing the stainless steel instruments.
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by nervesofsteel » Tue Nov 10, 2009 5:33 pm
B

10 sterilizations = 3.4 * Energy to manufacture
1 sterilization = .34 * Energy to manufacture

So B cannot be True..

Whts the OA..??
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Re: gmatprep

by Testluv » Tue Nov 10, 2009 8:40 pm
sq720 wrote:Certain instruments used in veterinary surgery can be made either of stainless steel or of nylon. In a study of such instruments, 10 complete sterilizations of a set of nylon instruments required 3.4 times the amount of energy used to manufacture that set of instruments, whereas 50 complete sterilizations of a set of stainless steel instruments required 2.1 times the amount of energy required to manufacture that set of instruments.
If the statements above are true, each of the following could be true EXCEPT:
(A) The 50 complete sterilizations of nylon instruments used more energy than did the 50 complete sterilizations of the stainless steel instruments.
(B) More energy was required for each complete sterilization of the nylon instruments than was required to manufacture the nylon instruments.
(C) More nylon instruments than stainless steel instruments were sterilized in the study.
(D) More energy was used to produce the stainless steel instruments than was used to produce the nylon instruments.
(E) The total cost of 50 complete sterilizations of the stainless steel instruments was greater than the cost of manufacturing the stainless steel instruments.
Hi sq720,

Here, the four wrong answers are things that could be true-the right answer is something that cannot be true (must be false).

The passage tells us that the ratio of energy required for sterilization to energy required for manufacture is greater for nylon instruments than it is for stainless steel instruments.

But we have no idea how much energy it takes to manufacture either of these. For example, it might take 1 unit of energy to manufacture a set of nylon instruments and 1000 units of energy to manufacture a set of stainless steel instruments. In that case, we would clearly need more energy to sterilize stainless steel than we would to sterilize nylon. And it could also be the other way around....So, both choices A and D could be true.

Choice C could be true because a "set" of nylon instruments could be 500 nylon instruments while a "set" of stainless steel could be 5 instruments.

Choice E could be true because we have no info about cost.

As nervesofsteel pointed out, Choice B cannot be true on the numbers. A sterilization of a set of nylon instruments only requires 34% of the energy required to manufacture that set. So, when sterilizing a set of nylon instruments, we will definitely need LESS energy than we did to manufacture that set.
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Re: gmatprep

by sunnyjohn » Tue Nov 10, 2009 9:37 pm
Testluv wrote:
.....
As nervesofsteel pointed out, Choice B cannot be true on the numbers. A sterilization of a set of nylon instruments only requires 34% of the energy required to manufacture that set. So, when sterilizing a set of nylon instruments, we will definitely need LESS energy than we did to manufacture that set.
Suppose :
energy required to manufacture one set of nylon instrument : 10 units.
so
10 instruments = 100 units.

energy for sterlization:
100*3.4 = 134
So:-
energy per unit for sterlization := 13.4

How can B be answer?
Am I doing any mistake? Please help me to correct..
Thanks.. :)
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Re: gmatprep

by Testluv » Tue Nov 10, 2009 10:15 pm
sunnyjohn wrote:
Testluv wrote:
.....
As nervesofsteel pointed out, Choice B cannot be true on the numbers. A sterilization of a set of nylon instruments only requires 34% of the energy required to manufacture that set. So, when sterilizing a set of nylon instruments, we will definitely need LESS energy than we did to manufacture that set.
Suppose :
energy required to manufacture one set of nylon instrument : 10 units.
so
10 instruments = 100 units.

energy for sterlization:
100*3.4 = 134
So:-
energy per unit for sterlization := 13.4

How can B be answer?
Am I doing any mistake? Please help me to correct..
Thanks.. :)
Hi sunnyjohn,

I think you might be mixing up sets and instruments, or maybe missing that the passage discusses 10 sterilizations whereas choice B discusses "each" sterilization.

The passage tells us: 10 complete sterilizations of a set of nylon instruments required 3.4 times the amount of energy used to manufacture that set of instruments.

In other words (numbers): 1 complete sterilization of a set of nylon instruments required 0.34 times the amount of energy used to manufacture that set of instruments.

So, the ratio in the passage is relating the energy required for TEN sterilizations to ONE manufacture of a set; whereas choice B talks about "each" complete sterilization, meaning one sterilization.

Suppose:
Energy required to manufacture ONE SET of nylon instruments is 10 units. (if there were 10 instruments in a set, this would be 1 unit per instrument)

We know 10 sterilizations of this set requires 3.4*10 = 34 units.

So, ONE sterilization of this set would be 1/10*34 = 3.4 units (if there were 10 instruments in a set, this would be 0.34 unit per instrument)

So, energy required to manufacture one set is 10 units; energy required to sterilize one set once is 3.4 units.

Therefore, EACH complete sterilization of a set requires LESS energy than was needed to make all of those nylon instruments.
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by sunnyjohn » Tue Nov 10, 2009 10:24 pm
got it completely..!
i was really confused with set and instrument..!
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by nervesofsteel » Wed Nov 11, 2009 2:35 am
forgot to mention

this is a very good question and it took me some time
to get the answer...
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by heshamelaziry » Wed Nov 11, 2009 6:53 pm
Thanks Testluv. Many CR questions on the test are difficult like this one. I don't know how to finish in 2 minutes.
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by Testluv » Wed Nov 11, 2009 9:57 pm
heshamelaziry wrote:Thanks Testluv. Many CR questions on the test are difficult like this one. I don't know how to finish in 2 minutes.
Well, you don't have to finish EVERY CR in 2 minutes. Some should take longer and some should take less time.

It is important to use the same technique every time, an accurate method that you know works; and to constantly practice it. If we know how to attack the question stem, characterize the answer choices; if we take our time analyzing the stimulus not rushing to the answer choices; and if we are familiar with the number vs proportion flaw that is commonly tested, then, in this question, we have significantly improved our chances of getting to the right answer efficiently (or eliminating the four wrong ones).

Here, we have to spend time analyzing the ratios in the passage thinking about what they mean. Step two of the Kaplan method for Inference questions tells us to determine what must be true AND what is not necessarily true. If we use that we are more likely to reach the big deduction that the passage is comparing energy of sterilization to energy required to manufacture and they give you a bunch of numbers BUT they never do mention the energy required to manufacture.
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