WillGetIt wrote:
Colorless diamonds can command high prices as gemstones. A type of less valuable diamonds can be treated to remove all color. Only sophisticated tests can distinguish such treated diamonds from naturally colorless ones. However, only 2 percent of diamonds mined are of the colored type that can be successfully treated, and many of those are of insufficient quality to make the treatment worthwhile. Surely, therefore, the vast majority of colorless diamonds sold by jewelers are naturally colorless.
A serious flaw in the reasoning of the argument is that
(A) comparisons between the price diamonds command as gemstones and their value for other uses are omitted
(B) information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless, gemstone diamonds
(C) the possibility that colored diamonds might be used as gemstones, even without having been treated, is ignored
(D) the currently available method for making colorless diamonds from colored ones is treated as though it were the only possible method for doing so
(E) the difficulty that a customer of a jeweler would have in distinguishing a naturally colorless diamond from treated one is not taken into account
Colourless diamonds are expensive.
Some coloured diamonds can be made colourless (and presumably sold at high price)
Only 2% of diamonds mined (including coloured and colourless) are treatable and even fewer (say just 1% of all diamonds mined) are good enough to make it worthwhile.
Conclusion: Vast majority of colourless diamonds sold by jewellers are naturally colourless.
There is a problem here. When we talk about the numbers 2% and 1%, we are talking about the set of all diamonds mined. In our conclusion, we are talking about the set of diamonds that are sold by the jewellers. Without knowing how big the set of diamonds sold by jewellers is, we cannot make the comparison.
Say total diamonds mined = 1000
Out of these, say 100 are naturally colourless.
Another 10 (1%) are coloured but profitably treatable.
So the jewellers could be selling 110 diamonds out of which the vast majority (100) could be naturally colourless.
Say total diamonds mined = 1000
Out of these, say 5 are naturally colourless.
Another 10 (1%) are coloured but profitably treatable.
So the jewellers could be selling 15 diamonds out of which the vast majority (10) are coloured but treated.
Hence, whether our conclusion works or not, depends on what % of all diamonds mined are naturally colourless.
(A) comparisons between the price diamonds command as gemstones and their value for other uses are omitted
Other uses are irrelevant.
(B) information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless, gemstone diamonds
Correct. As discussed above, we need info on rarity of naturally colourless diamonds to reach our conclusion.
(C) the possibility that colored diamonds might be used as gemstones, even without having been treated, is ignored
We are talking about colourless diamonds as gemstones. Irrelevant to our conclusion.
(D) the currently available method for making colorless diamonds from colored ones is treated as though it were the only possible method for doing so
We are talking about the current scenario only and the currently available method only.
(E) the difficulty that a customer of a jeweler would have in distinguishing a naturally colorless diamond from treated one is not taken into account
The argument says that only sophisticated tests can differentiate. This doesn't have anything to do with our conclusion.
Answer (B)
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