Q2 - A study of plaque buildup

[sumukh09]

This is a strengthen the argument question - we're asked to find an answer choice that helps support the conclusion and/or the reasoning that leads the author to make such a conclusion. Let's analyze the stim first. The core of this argument is:

group 3 used new toothbrush + groups 1 and 2 used same toothbrush ---> Group 3 had less plaque buildup at the end of the study than groups 1 and 2

Right off the bat you should be thinking, "why were the results different between group 3 and 1/2?"

Also, you should take note of the fact of the differences between the two groups that participated in the study; ie) the usage of a new and old toothbrush.

Answer choice B) helps explain why group 3 had less plaque buildup than the other two groups. It's because new toothbrushes have bristles that are stiff enough to inhibit the buildup of plaque.

A) is wrong because it only explains why group 1 might have had the plaque buildup - they didn't sterilize their brush every month. But this A/C leaves open the possibility that group 2 (who DID sterilize every month) could also have less plaque buildup. And of course, the conclusion says they had more than group 3.

C) Method is irrelevant

D) Only once a day? this might weaken the argument if anything

E) How vigorously they brushed is irrelevant, also it this A/C claims they brushed equally vigorously, so if anything, that should lead to equal amounts of plaque among the three groups.

[bbirdwell]

Actually, we wouldn't call this a strengthen question. We would call it an "explain the result" question. While these are similar to strengthen questions, they are distinct. Here, our task is to identify two facts from the stimulus that seem to contradict. Our answer choice should explain why both facts can be true.

Your question is right on -- a great strategy for working these problems is to formulate a question that says something like "Why X but Y?"

Here, we could say "Why did Group 3 have better results?"

(A) great explanation -- this is a partial answer. But it wouldn't explain why 3 had better results than 2. .

(B) New brushes are better! This is our answer

(C) Doesn't explain the result - all groups would be tested with the same method.

(D) attempts to make us think that Group 3 had greater gains because before the test they only brushed once a day. However, the test was not relative to people's previous plague levels -- it was merely a test of overall buildup.

(E) doesn't explain why 3 had better results.

[WaltGrace1983]

(D) attempts to make us think that Group 3 had greater gains because before the test they only brushed once a day. However, the test was not relative to people's previous plague levels -- it was merely a test of overall buildup.

Also (D)'s point is kind of moot because when the study began they all brushed twice a day. Thus, what they did before is not really relevant. It would be like measuring weight lost. Let's say we were competing to see who could lose the most weight on a new exercise routine over the course of three months. I lose 10 lbs and you lose 15 . Does it matter that I happened to exercise more than you before we started this competition? No. The competition had a definite beginning and a definite ending and during it we utilized the same workout routine.