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June 2007 - Sec 2 - LR - Q13

Video Transcript:

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Question 13: Standard aluminum soft-drink cans do not vary in the amount of aluminum that they contain. Fifty percent of
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the aluminum contained in a certain group (M) of standard aluminum soft drink cans was
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recycled from another group (L) of used, standard aluminum soft-drink cans. Since
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all the cans in L were recycled into cans in M and since the amount of
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material other than aluminum in an aluminum can
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is negligible, it follows that M contains twice as many cans as L.
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Argument or facts? Clearly we have an argument. The conclusion that 'it follows', our structural
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indicator. So M contains twice as many cans as L. And how do we know that?
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Well it tells us that fifty percent of the aluminum contained in a certain group (M). So, fifty
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percent of the aluminum in M was recycled from another group L
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of used standard aluminum soft drink cans. So we recycled L to make fifty percent of M. And then obviously the other 50%
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of (M) would be from something else. So that's what M is composed of. But now
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they're telling us that M is twice as many cans as L. So imagine L is X then M
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has 2X the amount of cans. So now that we have a clear understanding of this passage, again these would
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be the premises for the conclusion that M contains twice as many cans as L. You
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notice that this is flawed logic. This argument doesn't make any sense.
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The premise does not support this conclusion. And the question stem points that out by saying that
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conclusion of the argument follows logically if which of the following is
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assumed?
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Again, 'follows logically if'... We have a strengthen with sufficient premise question stem. So we are trying to guarantee
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the conclusion that M contains twice as many cans as L
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based on the premise that 50% of M came from recycling the cans in
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L. So let's take a look at (A): The aluminum in the cans of M cannot be recycled any
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further. That is completely irrelevant. It doesn't even strengthen this argument. So
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(A) is out. How does that help?
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(B) Recycled aluminum is of poorer quality than unrecycled aluminum. Again does not
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even strengthen this argument. What difference does that make? This is not an
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argument about the quality of the cans in M or L it's about the quantity. (C) all of the
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aluminum in an aluminum can is recovered when the can is recycled. Well if that's true then
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this 50% of M that came from L if L was X then all of the aluminum in an aluminum can is
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recovered when it's recycled. Again let's not forget that we recycled L into M.
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Well therefore, this 50% of M must be X. And if 50% of M is X then twice that would be 2X.
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You notice that would guarantee our conclusion. So (C) here would be correct
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answer. Again 100% guarantees the conclusion that M contains twice as many
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cans as L because if all of the aluminum in an aluminum can is recovered when
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recycled. And we recycled L and it gave us 50%. Well then M contains twice as many
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cans as L.
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But again just making sure... (D) none of the soft drink cans in group L had been made
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from recycled aluminum. Again completely irrelevant. So (D) would be out. Then
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lastly checking (E): Aluminum soft-drink cans are more easily recycled than are
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soft drink cans made from other materials. Again, what difference does that make?
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It's not about the ease of recycling it's about whether M contains twice as many cans
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as L. And again on a strengthen with sufficient premise we are trying to
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guarantee that conclusion
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100%.