I07-12

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"

Dbrunik · Answer

I think this is a  high-quality  question and I agree with explanation.

Bunuel · Answer

I have revised the question, solution, and formatting by adding more details to enhance clarity.

Arsh001 · Answer

For statement 2, we can see that the table is negatively correlated. So, how come true?

Bunuel · Answer

How exactly are rainfall (mm) and evaporation (mm) negatively correlated? 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. Does this pattern truly apply to rainfall and evaporation?

Here is a solution for the second statement:

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.

I07-12

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

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.