crackgmat007 wrote:This seems to be a very tricky question.
experts, help pls?
Hi guys,
The OA should be choice A.
The problem:
In Patton City, days are categorized as having heavy rainfall (more than two inches),
moderate rainfall (more than one inch, but no more than two inches), light rainfall (at
least a trace, but no more than one inch), or no rainfall. In 1990, there were fewer days
with light rainfall than in 1910 and fewer with moderate rainfall, yet total rainfall for the
year was 20 percent higher in 1990 than in 1910.
If the statements above are true, then it is also possible that in Patton City
A. the number of days with heavy rainfall was lower in 1990 than in 1910
B. the number of days with some rainfall, but no more than two inches, was the same
in 1990 as in 1910
C. the number of days with some rainfall, but no more than two inches, was higher in
1990 than in 1910
D. the total number of inches of rain that fell on days with moderate rainfall in 1990
was more than twice what it had been in 1910
E. the average amount of rainfall per month was lower in 1990 than in 1910
The Kaplan method tells us to read the question stem first. The question stem tells us to select a choice that is "possible." Because the right answer is something that is possible (could be true), the four wrong answers are impossible (must be false).
Before we even think about approaching the answer choices, we should analyze the stimulus, determining everything that must be true (and what does not necessarily have to be true). (Step 2 of Kaplan method for inference questions).
There are four kinds of days:
1) days with no rainfall;
2) days with light rainfall, which is more than zero up to (and inlcuding) one inch;
3) days with moderate rainfall, which is more than one and up to (and including) two inches; and
4) days with heavy rainfall, which is anything more than two inches.
In 1990, there were fewer days with light and moderate rainfall than in 1910. Also, in 1990, there was more total rainfall. This does not necessarily mean that there were more heavy rainfall days in 1990. Remember, we're talking ranges here. All of the light days in 1910 could have been close to zero while all of the light days in 1990 could have been closer to one. So, the excess rain in 1990 could be due either to more heavily rainy days or else the light and moderate days being more "rainy" than they were in 1910.
...Therefore, choice A could be true or is possible (matches the above deduction). Because we've found a match to our prediction, and because there can be only one credited response, we are done. Seriously, you are better off taking an extra moment confirming that this could be true, then trying to prove that the other four choices must be false (or impossible). You don't get rewarded for figuring four reasons why four wrong answers are wrong. (Steps 3 and 4 are predict and match).
But let's look at the other choices:
B. the number of days with some rainfall, but no more than two inches, was the same
in 1990 as in 1910.
These are the days with light and moderate rainfall. There were more of these days in 1910 than in in 1990. Therefore, this must be false (impossible).
C. the number of days with some rainfall, but no more than two inches, was higher in
1990 than in 1910.
This choice must be false for the same reason that chocie B must be false.
D. the total number of inches of rain that fell on days with moderate rainfall in 1990
was more than twice what it had been in 1910.
This is mathematically impossible. We know there are fewer moderatley rainy days in 1990 than in 1910, and the range is less than one inch. Even if we were to maximize moderate rainy days in 1990 and minimize in 1910, and minimize rain per moderately rainy day in 1910 while maximizing rain per moderately rainy day in 1990, this is still impossible. For example, let's say there are 11 moderately rainy days in 1910 with 1.1 inch per day, and 10 moderately rainy days in 1990 with 2.0 inches per day. Then we would have 11*1.1 = 12.1 inches of rainfall on moderately rainy days in 1910 while we would have 10*2.0 = 20 inches of rainfall on moderately rainy days in 1990. It is impossible that the rainfall on moderately rainy days in 1990 is more than twice as great as the amount of rain that fell on moderately rainy days in 1910.
Therefore, choice D must be false, or is impossible.
(But see how long that took to figure out? Honestly, process of elimination is not efficient).
Finally, choice E:
E. the average amount of rainfall per month was lower in 1990 than in 1910
Because the total amount of rain in 1990 was greater than it was in 1910, then the average rainfall per month will also be greater. For example, if total rainfall in 1910 was 100 and in 1990 was 120 (20% greater), then obviously 120/12 is greater than 100/12. Therefore, this choice also must be false (impossible).
Choose A.
