The table below shows various measurements reported monthly over a two

Question

The table below shows various measurements reported monthly over a two-year period at Lake Molono, from April 2005 to March 2007. 
   Date 
 Average Water Level (m) 
 Average Surface Area (m^2) 
 Rain (mm) 
 Evaporation (mm) 
 Net Groundwater (mm) 
 
  Apr-2005 
 32.50 
 568,959 
 101 
 160 
 8 
 
  May-2005 
 32.45 
 566,330 
 129 
 151 
 5 
 
  Jun-2005 
 32.42 
 565,347 
 427 
 126 
 70 
 
  Jul-2005 
 32.83 
 582,543 
 149 
 153 
 126 
 
  Aug-2005 
 32.96 
 587,751 
 247 
 164 
 103 
 
  Sep-2005 
 33.18 
 595,213 
 83 
 144 
 87 
 
  Oct-2005 
 33.20 
 596,118 
 241 
 136 
 55 
 
  Nov-2005 
 33.40 
 602,133 
 38 
 80 
 73 
 
  Dec-2005 
 33.43 
 603,039 
 38 
 73 
 63 
 
  Jan-2006 
 33.45 
 603,755 
 13 
 69 
 24 
 
  Feb-2006 
 33.40 
 602,224 
 62 
 74 
 -1 
 
  Mar-2006 
 33.37 
 601,399 
 4 
 124 
 -1 
 
  Apr-2006 
 33.21 
 596,317 
 24 
 161 
 -18 
 
  May-2006 
 33.02 
 589,852 
 65 
 170 
 -36 
 
  Jun-2006 
 32.86 
 583,728 
 122 
 170 
 -19 
 
  Jul-2006 
 32.78 
 580,489 
 124 
 154 
 -26 
 
  Aug-2006 
 32.71 
 577,886 
 152 
 170 
 -39 
 
  Sep-2006 
 32.65 
 575,210 
 149 
 146 
 -52 
 
  Oct-2006 
 32.59 
 572,859 
 22 
 145 
 -64 
 
  Nov-2006 
 32.38 
 563,357 
 16 
 91 
 -48 
 
  Dec-2006 
 32.24 
 556,601 
 127 
 66 
 -57 
 
  Jan-2007 
 32.24 
 556,601 
 51 
 79 
 -56 
 
  Feb-2007 
 32.14 
 551,711 
 63 
 73 
 -53 
 
  Mar-2007 
 32.07 
 548,103 
 16 
 118 
 -83

For each of the following statements, select  True  if the statement can be verified to be true based on the information provided. Otherwise, select  False .

Bunuel · Answer

Official Solution: Statement 1: Two data sets are positively correlated if they both tend to be higher in the same cases. They are negatively correlated if one tends to be higher in cases where the other is lower. For positively correlated data, their lines tend to slope up or down together; the more consistently this happens, the stronger the positive correlation. Conversely, when two data sets are negatively correlated, the line for one tends to slope up while the other slopes down, and vice versa. The more consistently these opposite slopes occur, the stronger the negative correlation. Thus, this statement is True. Examining the table, we observe that the average water level and the average surface area move in the same direction; whenever one increases, the other also increases, and vice versa. Thus, we can conclude that the data are positively correlated. Statement 2: Examining the table, we observe that, in most cases, rainfall (mm) and evaporation (mm) do not move in opposite directions: when one increases, the other does not always decrease, and vice versa. Thus, we can conclude that the data are not negatively correlated. Thus, this statement is False. Statement 3: Sorting by rainfall, we observe that in Dec-2006, rainfall was more than 100 mm (127 mm), while evaporation was less than 100 mm (66 mm). Thus, this statement is False. Correct answer: The average water level (m) and the average surface area (m^2) were positively correlated during the two-year period. "True" Rainfall (mm) and evaporation (mm) were negatively correlated during the two-year period. "False" Every month with rainfall exceeding 100 mm also had evaporation exceeding 100 mm. "False" GMAT-Club-Forum-t30019k6.png

Bismuth83 · Answer

1. The question asks us to  check whether the following statements are true or false .

2.  The average water level (m) and the average surface area (m^2) were positively correlated during the two-year period.  Let's check for each interval between months: + + + + + + + + + + + + + + + + + + + + 0 + +. The two values are clearly positively related.   So, this statement is true.
  
3.  Rainfall (mm) and evaporation (mm) were negatively correlated during the two-year period.  Let's check for each interval between months: - - - + + - + 0 + + - + + 0 - + + + + - - - -. The two values are clearly not negatively related (most likely are unrelated).   So, this statement is false.

4.  Every month with rainfall exceeding 100 mm also had evaporation exceeding 100 mm.  December 2006 had rainfall at 127 (>100), however evaporation was 66 (100<).   So, this statement is false.

Aalto700 · Answer

why this 700+ level ? Bunuel

Bunuel · Answer

The difficulty level of a question on the site, after sufficient attempts, is determined automatically based on various parameters collected from users' attempts via timer, such as the percentage of correct answers and the time taken to answer the question. So, this is a hard question based on our statistics.

AAYUSHI4 · Answer

in statement 2, one is going up and other is going down- means negative correlation then why the answer is false?  Bunuel .

Bunuel · Answer

One or two instances where one goes up and the other goes down does  not  establish negative correlation.

As explained in the solution, negative correlation means a  consistent pattern: w hen one increases, the other  generally  decreases across the data.

Here, if you scan the table , rainfall and evaporation do  not  consistently move in opposite directions. Sometimes both go up, sometimes both go down, sometimes they move differently.

So there is  no clear overall inverse pattern , which is why the statement is False.

EpicKnot · Answer

During Assessing Statement I, the avg water level between period Nov'05 to Feb'06 remains the same while the avg surface area increases. The questions asks us to establish whether a positive correlation exists meaning in all scenarios, if one go up, the other does too which does not follow during the above period. But still, the answer is true. Why is so? Can we take general pattern while answering such questions?

Bunuel · Answer

I believe this is addressed in the solution. Positive correlation does  not  mean that the two values must move in the same direction in  every  interval.

It means that,  overall , higher values of one variable tend to be associated with higher values of the other variable, and lower values of one tend to be associated with lower values of the other. So we should look at the  general pattern  across the data set, not treat one limited comparison as enough to reject positive correlation.

The table below shows various measurements reported monthly over a two

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Date	Average Water Level (m)	Average Surface Area (m^2)	Rain (mm)	Evaporation (mm)	Net Groundwater (mm)
Apr-2005	32.50	568,959	101	160	8
May-2005	32.45	566,330	129	151	5
Jun-2005	32.42	565,347	427	126	70
Jul-2005	32.83	582,543	149	153	126
Aug-2005	32.96	587,751	247	164	103
Sep-2005	33.18	595,213	83	144	87
Oct-2005	33.20	596,118	241	136	55
Nov-2005	33.40	602,133	38	80	73
Dec-2005	33.43	603,039	38	73	63
Jan-2006	33.45	603,755	13	69	24
Feb-2006	33.40	602,224	62	74	-1
Mar-2006	33.37	601,399	4	124	-1
Apr-2006	33.21	596,317	24	161	-18
May-2006	33.02	589,852	65	170	-36
Jun-2006	32.86	583,728	122	170	-19
Jul-2006	32.78	580,489	124	154	-26
Aug-2006	32.71	577,886	152	170	-39
Sep-2006	32.65	575,210	149	146	-52
Oct-2006	32.59	572,859	22	145	-64
Nov-2006	32.38	563,357	16	91	-48
Dec-2006	32.24	556,601	127	66	-57
Jan-2007	32.24	556,601	51	79	-56
Feb-2007	32.14	551,711	63	73	-53
Mar-2007	32.07	548,103	16	118	-83

True	False
		The average water level (m) and the average surface area (m^2) were positively correlated during the two-year period.
		Rainfall (mm) and evaporation (mm) were negatively correlated during the two-year period.
		Every month with rainfall exceeding 100 mm also had evaporation exceeding 100 mm.

GMAT Graphs and Tables (G&T) Questions

The table below shows various measurements reported monthly over a two

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