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

Question

The table shows, for each of 10 Irish weather stations and each of 8 calendar months, the average (arithmetic mean) number of days per month that the station recorded snowfall during the years 1961–2000. For example, during this time period, the station at Birr recorded snowfall on an average of 4.5 days in January.

Station    Jan    Feb    Mar    Apr    May    Oct    Nov    Dec     Belmullet  4.6  4.3  3.5  1.7  0.2  0.0  0.7  2.7    Birr  4.5  3.3  2.5  1.0  0.2  0.0  0.5  2.5    Claremorris  6.5  5.3  4.5  1.9  0.2  0.1  1.6  3.6    Clones  6.2  5.8  4.4  1.8  0.4  0.1  1.6  3.8    Cork  3.9  4.1  2.6  1.1  0.1  0.0  0.5  2.4    Dublin  5.6  5.0  3.8  1.6  0.3  0.1  0.9  3.0    Kilkenny  4.5  4.3  2.7  0.9  0.1  0.0  0.5  2.4    Mullingar  6.0  5.3  3.9  2.0  0.2  0.0  1.0  3.5    Rosslare  2.3  3.1  1.6  0.7  0.1  0.0  0.2  1.1    Valentina  1.3  1.4  1.0  0.4  0.1  0.0  0.1  0.8

For each of the following statements about the weather stations listed in the table, select  Must be true  if that statement must be true if the information provided is correct. Otherwise, select  Might not be true .

ID: 700220

chetan2u · Accepted Answer

1. 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 month. Claremorris has the greatest average number of days, which is 6.5 
However, when you compare the averages every month of Claremorris with Clones, you can easily make it the averages are more for clones. We do not require to multiply number of days with the averages to get to the answer. The gap in the avergaes between the two stations cannot be covered by minor variations in days in months of a year.
 Hence, 'Might not be true' is the answer.
 
2. Cork had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000.
The average over a month cannot tell us about the rains on the individual days.
 Clearly, need not be true.
 
3. 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 had average rainfall of 1.3 and 1.4 in Jan and Feb. If rainfall was recorded on only one day each Feb every year, then the average would be 1 or less. 
But 1.3 means, there were some years when the rains were there on at least 2 days.
 Must be true

Sans8 · Answer

chetan2u 
I didn't get your 3rd explaination: Why  If rainfall was recorded on only one day each Feb every year, then the average would be 1 or less?
Can you explain this in a bit detail

chetan2u · Answer

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.

rashes · Answer

Hi Chetan,  chetan2u

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

chetan2u · Answer

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

Nidhibatra · Answer

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

KarishmaB · Answer

Video discussion on this question: https://youtu.be/Ucf5Q-IJbQ8 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/

playthegame · Answer

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.

Gemmie · Answer

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. => Might not be true

Sort column Jan => Claremoris hass the greatest avg number of rainfall days in Jan

However, regarding the total number of rainfall days all months, Clones seem to have more
 
Jan: -.3
Feb: +.5
Mar: -.1
Apr: -.1
May: +.2
Oct-Nov: same
Dec: +.2
 
>> +.9 -.5 = +.4

Cork had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000. => Might not be true

We only know the avg rainfall days in Feb of Cork is 4.1

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.=> Must be true

Valentia had average rainfall of 1.3 in Jan => There must be a year when Valentia had at least 2 rainfall days in Jan

SR4896 · Answer

Is partial marking for correct answers given?

tuyaras · Answer

No partial marking for correct answers given.....That's why it is so hard to get a mark in DI section.

tuyaras · Answer

Q3: Can we infer that Valentia has average 1.3*31 = 4.03 snow fall days in January during 1961–2000 ?

PeachSnapple1 · Answer

There is a typo in the third option  Valentia  recorded 2 or more days of snowfall in a single calendar month.] The table only has  Valentina . Never know an OG question could have a typo.

PeachSnapple1 · Answer

Fairly easy question if you nail the average concept. Took me sub one minute.

1. 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. 
The table is missing four months, so we can't infer   -->  Might not be true

2. Cork had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000. 
We only know Cork's average Feb snowfall is 4.1 for the whole 40 years, so we cannot infer that  each year  there was least one snow day. Could be the case that some years had 0, and the rest of the years have huge amount of snow days. -->  Might not be true

3. 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. 
Assuming the number of snow day was an integer number, if an average of snow days in any month in Valentina was greater than 1 (1.1, 1.2, 1.3, etc) then there must have been some year with at least 2 days of snow -->  must be true

amoeba99 · Answer

For option 3 -

Because each year the number of days for which there was recorded snowfall for any given month had to be a whole number

This seems like an assumption which was not implied. It could have been very well understood from question stem that the number of days could be a decimal for a given month, for example it snowed for 1.5 days. This invalidates the logic for option 3.

Bunuel · Answer

Snowfall days must be integers because you either have snow on a day or you don’t, there’s no such thing as half a day recorded.

deva1 · Answer

Can anyone clarify why question 1 can't be true? I'm just confused. Of course, when I compare Claremorris with Clones, I can get that some month in clones is higher than Claremorris.

Bunuel · Answer

Have you checked the replies above? https://gmatclub.com/forum/the-table-sh ... l#p3369768 https://gmatclub.com/forum/the-table-sh ... l#p3392742 https://gmatclub.com/forum/the-table-sh ... l#p3401489 ...

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

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Station	Jan	Feb	Mar	Apr	May	Oct	Nov	Dec
Belmullet	4.6	4.3	3.5	1.7	0.2	0.0	0.7	2.7
Birr	4.5	3.3	2.5	1.0	0.2	0.0	0.5	2.5
Claremorris	6.5	5.3	4.5	1.9	0.2	0.1	1.6	3.6
Clones	6.2	5.8	4.4	1.8	0.4	0.1	1.6	3.8
Cork	3.9	4.1	2.6	1.1	0.1	0.0	0.5	2.4
Dublin	5.6	5.0	3.8	1.6	0.3	0.1	0.9	3.0
Kilkenny	4.5	4.3	2.7	0.9	0.1	0.0	0.5	2.4
Mullingar	6.0	5.3	3.9	2.0	0.2	0.0	1.0	3.5
Rosslare	2.3	3.1	1.6	0.7	0.1	0.0	0.2	1.1
Valentina	1.3	1.4	1.0	0.4	0.1	0.0	0.1	0.8

Must be true	Might not be true
		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.
		Cork had at least 2 days with recorded snowfall during February in each of the years from 1961 through 2000.
		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.

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

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