In Patton City, Days are Categorized as Having Heavy Rainfall.

Topic: 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

In Patton City, Days are Categorized as Having Heavy Rainfall. – is a GMAT Critical question. This particular GMAT Critical Reasoning topic has been taken from the book ‘GMAT Official Guide Verbal Review’. This weakens the argument type of the GMAT CR question. To answer the question, a candidate can either find a piece of evidence that would weaken the argument or have logical flaws in the argument. GMAT critical reasoning tests the logical and analytical skills of the candidates. This topic requires candidates to find the strengths and weaknesses of the argument, or find the logical flaw in the argument. The GMAT CR section contains 10 -13 GMAT critical reasoning questions out of 36 GMAT verbal questions.

Answer: A
Explanation: Let us check the question. As per the problem statement:

HR > 2
MR 1 to 2
LR 0 to 1
No Rain 0
LR Days (1990) < LR Days (1910)
MR Days (1990) < MR Days (1910)

So, Total rainfall 1990 > Total rainfall 1910

Now let us analyze the assumptions:

1. the number of days with heavy rainfall was lower in 1990 than in 1910

We can see that though HR Days (1990) < HR Days (1910), 1990 have had higher total rainfall. Let us consider that if in 1990, HR days were fewer. Then on each one of those days, it rained 50 inches whereas in 1910. Next on HR Days were more but on each one of those days. It rained only 3 inches, then total rainfall in 1990 could be higher than that of 1910. So option A is the correct answer.

2. the number of days with some rainfall, but no more than two inches, was the same in 1990 as in 1910.

This is an incomplete assumption, as we can see that 
LR Days (1990) < LR Days (1910)
MR Days (1990) < MR Days (1910)
So LR Days (1990) + MR Days (1990) < LR Days (1910) + MR Days (1910)

100. the number of days with some rainfall, but no more than two inches, was higher in 1990 than in 1910

This an incomplete assumption. 

500. 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

In option D if we consider that on a moderate rainfall day, the amount of rainfall is more than 1. But it is less than 2 than other days. If the number of MR days in 1990 is less than the number of MR days in 1910. Hence, no amount of rain can make the total rainfall more than twice. Hence option D is not correct. 

5. the average amount of rainfall per month was lower in 1990 than in 1910

This assumption is insufficient, as
Total rain (1990) > Total rain (1910)
Average rain per month equals (Total rain)/12
Total rain (1990)/12 > Total rain (1910)/12

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