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The following is an English comprehension task, and we can't agree upon the correct answer. According to the textbook, answer B is correct. However, in my opinion, it is clearly lacking the word not. If the word "not" is put in, then it makes sense - otherwise it doesn't make sense for me. Could a native speaker confirm this?

  1. Attention Deficit Disorder (ADD) is a condition characterized by an Inability to focus on any topic for a prolonged period of time, and is especially common among children five to ten years old. A recent study has shown that 85 percent of seven-year-old children with ADD watch, on average, more than five hours of television a day. It is therefore very likely that Ed, age seven, has ADD, since he watches roughly six hours of television a day.

The argument above is flawed because it:

(A) cites as a direct causal mechanism a factor that may only be a partial cause of the condition in question

(B) fails to indicate the chances of having ADD among seven-year-old children who watch more than five hours of television a day

(C) limits the description of the symptoms of ADD to an inability to focus for a prolonged period of time

(D) fails to consider the possibility that Ed may be among the 15 percent of children who do not watch more than five hours of television a day

(E) does not allow for other causes of ADD besides television watching

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Where are you trying to put 'not'? –  simchona Sep 9 '11 at 19:59
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I'd say A, B, and E would be correct, with a preference for A and B, which seem to say the same thing, over E, which says the same thing less precisely. C is hardly relevant, and D is not really true, because the argument includes this caveat with it is therefore likely that.... –  Cerberus Sep 9 '11 at 20:03
    
i'd put: fails to indicate the chances of NOT having ADD among... –  Mat Sep 9 '11 at 20:05
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It's a bit "sly" to omit the word NOT. Logically it makes no difference to the fact that (B) is the only correct answer. All the other points are either irrelevant or untrue, and it is a truism that if you know "the chances of something being true" you automatically know the chances of it being untrue. But OP's reaction is understandable, in that if anyone wanted to dispute the argument, they would almost certainly want to raise the possibility that the "NOT chances" might actually be more than half, in which case Ed probably wouldn't have ADD. –  FumbleFingers Sep 9 '11 at 21:21
    
@Cerberus: A and E are "true" statements, but they have no bearing on whether the argument itself is logically flawed. In that respect they're simply irrelevant, the same as C. On the other hand, D is nonsensical - there is no possibility that Ed is in that 15% who watch less than 5 hours, since we're told he watches about 6. –  FumbleFingers Sep 9 '11 at 21:28
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2 Answers

up vote 5 down vote accepted

(B) is correct as worded, but it would also be correct if it said "not having ADD".

In order to make a judgment concerning Ed, you need a statistic which tells what percentage of children who watch >5 hours of TV per day have (or what percentage does not have) ADD.

Here you see that though most 7-year-olds with ADD watch >5 hours of TV per day, most 7-year-olds who watch >5 hours of TV per day do not have ADD:

7yo

All we know is that Ed is in the large circle. We have no way of telling how likely it is that he is also in the small circle. (B) is correct in stating that you need to know how many children in the large circle are (or how many are not) in the small circle. The exercise only gives the ratio of the blue to the green area, which is immaterial.

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ok got it. not stating the chances of having ADD is the same as not stating the chances of NOT having ADD. the text lacks both, which is stated in B. thank you! –  Mat Sep 9 '11 at 20:37
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It's B. The other ones are worded to confuse; pay specific attention to the "therefore" clause. It suggests that Ed must have ADD because he watches greater than 5 hours of TV per day, when the premises given would only suggest that a boy who had ADD would watch at least 5 hours of TV per day - more like the converse of the proposed conclusion. The premise required for the proposed conclusion is never given in the paragraph.

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that's why the conclusion is wrong - they don't consider the fact that a seven years old boy who watches six hours of television might NOT have ADD. so the word 'NOT' is missing in be –  Mat Sep 9 '11 at 20:15
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@Mat: it fails to indicate the chances of having OR not having ADD for any children at all. The only chances it indicates is the chances of watching tv IF you have ADD. –  Mr. Shiny and New 安宇 Sep 9 '11 at 20:21
    
Mat, @Mr. Shiny is correct. Neither was considered, both are relevant, and only one was a choice - or could have been, in a mutually-exclusive context such as this - and as such, B is correct. –  Rae Sep 9 '11 at 20:26
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