The table shows, for each of 10 Irish weather stations and each of 8 c

Jan and feb have an average of 1.3 and 1.4. Let us take Feb.
average of 1.3 days means rainfall was 1.3 *40 or 52 days.
We can distribute 40 out of these 52 days 1 per year. But what happens to remaining 52-40 or 12 days. They have to be adjusted in these 40 years, so some day would surely have rain more run 1 day.­

­Hi Chetan, ­chetan2u

I still am not able to understand where did you get this 40 or 52 logic­

­

The average days are 1.3 per year. So over 40 years , total days it rained would be 1.3*40 or 52 days.
If you try to minimise rain per year, you will distribute one day per year, so 40 days out of 52 days gone. But what about remaining 52-40 or 12 days. If you distribute these to some months, surely some month would have at least 2 days rain.

rashes
Posted from my mobile device­

Why is it that it cannot rain for 1.3 days in a particular month, why are we assuming that it necessarily has to be a full day of rain

Posted from my mobile device

­
Some of the toughest DI questions are based on averages or weighted averages, as is this. Once you realise this and learn to navigate through it, the question becomes a whole lot easier and quicker. 

The station with the greatest average number of days of recorded snowfall during January of years 1961 through 2000 had the greatest total number of days with recorded snowfall during those years.

Sort the table by Jan. Claremorris has maximum avg days of snowfall in Jan. But does it have maximum total number of days of rainfall too? 
Coompare with Clones which is right above it - a possible candidate with fewer days of snow than Claremorris in some months and more days in other months. 
Go month by month - Clones has 0.3 less in Jan, .5 more in Feb so 0.2 more till now. .1 less in March so .1 less till now. and so on. 
We see that Clones has higher average number of days of snow. So Claremorris certainly is not the one with the highest total number of days of snow. 

ANSWER: Might Not be True


Cork had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000.

Cork had on average 4.1 days of snow every year in Feb. But this is just the average. It is possible that in some years, it had no snow in Feb. 
Hence, it is not necessary that it had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000.

ANSWER: Might Not be True

In at least one year from 1961 through 2000, the station at Valentia recorded 2 or more days of snowfall in a single calendar month.

Valentia recorded average of 1.3 days of snow in Jan. This means in some years, it would have recorded 2 or more days of snow. If that were not the case and in each year it had recorded only 0 or 1 day of snowfall in Jan, then the average could not have been 1.3. 
Hence it is necessary that in at least one year from 1961 through 2000, the station at Valentia recorded 2 or more days of snowfall in a single calendar month.

ANSWER: Must be True

Here is a video discussing how to solve for average: https://youtu.be/W-qhIZ29UIs

Here is post that discusses the deviation concept: https://anaprep.com/arithmetic-usefulness-of-deviations/­

Official Guide Explanation

RO 1, The station with the greatest average number of days of recorded snowfall… had the greatest total number of days of recorded snowfall…:
Sort the Jan column to find that the station with the greatest average number of days of recorded snowfall in January was Claremorris. Did Claremorris have the greatest total number of days with recorded snowfall during those years? Note that the table lists statistics for only 8 months. Therefore, because it is possible that one of the stations had snowfall in at least one of the months not shown in table, we cannot determine which station had the greatest total number of days with recorded snowfall during those years. (Additionally, note that if we consider only the months included in the table, Clones’s total number exceeds Claremorris’s.)

The correct response is Might not be true.

RO2, Cork had at least 2 days with recorded snowfall during February in each of the years…:
We know that Cork averaged 4.1 days of recorded snowfall in February over the 40-year period from 1961–2000, which means there was a total of 164 days of recorded snowfall over that period. We cannot infer how those days were distributed over those years. For instance, it is possible that in 32 years it snowed 5 days and in another year, it snowed 4 days, and in the remaining 7 years it there were no days with snow, in which case it would not be true that Cork had at least 2 days with recorded snowfall during February in each of the years of the 40-year period.

The correct response is Might not be true.

RO3, In at least one year … the station at Valentia recorded 2 or more days of snowfall in a single calendar month:
In both January and February, Valentia averaged 1.3 and 1.4 days of recorded snowfall, respectively. Because each year the number of days for which there was recorded snowfall for any given month had to be a whole number (that is, it cannot be that in, say, 1986 there was 1.3 days for which there was recorded snow fall; either there was 1 day, or 2 days, or 3 days, etc.). Therefore, for any month for which the average number of days of recorded snowfall is greater than 1, there had to be at least 2 days of recorded snowfall in at least one of the years.

The correct response is Must be true.