Q:

English comprehension task

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?

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

A:

(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:

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.

