several GWD questions...

GWD-9-Q13:

Fact: Asthma, a bronchial
condition, is much less common ailment than hay fever, an allergic inflammation
of the nasal passages.

Fact: over 95 percent of
people who have asthma also suffer from hay fever.

If the information given as
facts above is true, which of the following must also be true?
 

1. Hay fever is a prerequisite for the development
        of asthma
2. Asthma is a prerequisite for the development of
        hay fever
3. Those who have neither hay fever nor asthma
        comprise less than 5 percent of the total population
4. The number of people who have both of these
        ailments is greater than the number of people who have only one of them
5. The percentage of people suffering from hay fever
        who also have asthma is lower than 95 percent.

GWD-9-Q37:

Researchers
took a group of teenagers who had never smoked and for one year tracked whether
they took up smoking and how their mental health changed. Those who began smoking
within a month of the study’s start were four times as likely to be depressed
at the study’s end than those who did not begin smoking. Since nicotine in
cigarettes changes brain chemistry, perhaps thereby affecting mood, it is
likely that smoking contributes to depression in teenagers.

Which
of the following, if true, most strengthens the argument?

1. Participants who were depressed at the study’s
        start were no more likely to be smokers at the study’s end than those who
        were not depressed.
2. Participants who began smoking within a month of
        the study’s start were no more likely than those who began midway through
        to have quit smoking by the study’s end.
3. Few, if any, of the participants in the study
        were friends or relatives of other participants.
4. Some participants entered and emerged from a
        period of depression within the year of the study.
5. The researchers did not track use of alcohol by
        the teenagers.

GWD-9-Q38:

In
January of last year the Moviemania chain of movie theaters started propping
its popcorn in canola oil, instead of the less healthful coconut oil that it
had been using until then. Now Moviemania is planning to switch back, saying
that the change has hurt popcorn sales. That claim is false, however, since
according to Moviemania’s own sales figures, Moviemania sold 5 percent more
popcorn last year than in the previous year.

Which
of the following, if true, most strongly supports the argument against Moviemania’s
claim?

1. Total sales of all refreshments at Moviemania’s
        movie theaters increased by less than 5 percent last year.
2. Moviemania makes more money on food and beverages
        sold at its theaters than it does on sales of movie tickets.
3. Moviemania’s customers prefer the taste of
        popcorn popped in coconut oil to that of popcorn popped in canola oil.
4. Total attendance at Moviemania’s movie theaters
        was more than 20 percent higher last year than the year before.
5. The year before last, Moviemania experienced a 10
        percent increase in popcorn sales over the previous year.

 Why D?

thanks a lot!

GWD-9-Q13:

A+F >95%A, and A<F --> A+F <95%F

Note A is much less than F, say F=100%, A=90%. The conclusion stands.

GWD-9-Q37:

Hidden assumption: it is smoking, rather than passive smoking, that causes the depression.

Choice C excludes some of such passive smoking possibilities (ie.it is more likely to be affected by the smoking participants if the others are their friends), thereby strengthening the argument.

GWD-9-Q38:

Hidden assumption: attendence change leads to the change in the popcorn sales. Now the discrepancy in the change rate confirms a possible interference of the porduct type.

Thank you so much for your answers, davidli8888! They are really helpful. However, I don't quite understand the answer for this question. Would you please explain more about it?

Thanks a lot!