georgina1107

A is correct

There are only two likely possibilities for 1990 to have more total rainfalls than 1910:

1) Total rainfalls from heavy rainfalls is bigger in 1990 than in 1910.  This could be done either by very heavy rains in a few days in 1990 or with more heavy rainfalls days in 1990
2) Total rainfalls from moderate/light rainfalls is bigger in 1990 than in 1910.  This possibility sounds counterintuitive but is mathmatically possible.  Keep in mind the definition of moderate/light rainfalls is based on a range. It is conceivable that a moderate rainfalls day could have either 1.9 inch or 1.1 inch of rain.  So if all the moderate rainfall days in 1990 had 1.9 inch while all the moderate rainfall days in 1910 had only 1.1 inch, the total rainfall in 1990 could be bigger than in 1910.

Answer A points out the first possibility and is the right answer.

georgina1107

I was leaning to D at first.  But the math shows that it is impossible to have twice amount of rain with even the same number of moderate rainfall days.  So I crossed out answer D.  If D says the light rainfall amount in 1990 is twice that in 1910, that would be possible.