Researchers studying long-term changes in regional mouse populations h

Question

Researchers studying long-term changes in regional mouse populations have found that by focusing on the populations of a rare but widespread and easily identifiable species of mouse (Species X), they can make fairly accurate estimations about the total regional mouse populations.

In a report on a recent study that included the data tables that follow, the researchers provided some addenda:

1. The Species X population of Region CV increased by 123,995 between 1990 and 2005.

2. In contrast, the Species X population of Region EW declined by about 52% during that same time.

chetan2u · Accepted Answer

Frankly speaking, I was initially lost with the words.

3. Assume that the  Species X population totals of TY  remained roughly constant between 1990 and 2005. Which one of the following statements is best supported by the information provided?

Not the best of the wordings one should find in an official question but the solution would lie in the sentence.

Here, the species X population roughly remainded constant from 1960 to 1990, from 947630 to 968460. But this amount reduce to 2.1% from 3.5% of total mouse poulation.

Thus, constant population of species X means increase in overall mouse population in TY.
Correct option - The total mouse population of TY may not have remained roughly constant between 1990 and 2005.

nazii · Answer

For question 1
In order to find the total mouse in a region , we have to divide the given number of X to the percentage provided in the second table
1. 1960: 947/3.356= 282
1975:144/0.351= 410
1990:968/2.051= 478
we can see difference between 1960 and 1975 is more. so answer is yes
second part: from the last section we got the total population for 1990, which was about 478, therefore this is also YES.
third part: again looking back to the calculation we did, it it obvious that from 1975 to 1990, the poulation increased (from 410 to 478), the answer is No

Piscine15 · Answer

3rd Question:

If their numeral value remained the same from 1990 to 2005, then we can say that maybe their total population not remained the same as species X is A percent of total population.

Hence if total population is increased then surely the A value is decreased accordingly to make the effect constant (i.e. X population in 2005) and vice versa.

.
.

We can also say that all other options are getting rejected easily. A and E are directly out.

steck · Answer

To find the total number of mice in a region, we need to divide the given number of "X" by the percentage provided in the second table. Let's calculate the values:

For the year 1960:
Given number of X: 947
Percentage: 3.356%
Total number of mice in 1960 = 947 / 3.356 = 282 (rounded to the nearest whole number)

For the year 1975:
Given number of X: 144
Percentage: 0.351%
Total number of mice in 1975 = 144 / 0.351 = 410 (rounded to the nearest whole number)

For the year 1990:
Given number of X: 968
Percentage: 2.051%
Total number of mice in 1990 = 968 / 2.051 = 472 (rounded to the nearest whole number)

Based on these calculations, we can observe that there is an increase in the total number of mice from 1960 to 1975 (282 to 410). Therefore, the answer to the first part of the question is "Yes."

For the second part of the question, we can see that the total population of the region in 1990 is approximately 478 (as calculated above). Since this is greater than the total number of mice in 1990 (472), the answer is also "Yes."

However, for the third part of the question, if we compare the total number of mice in 1975 (410) to the total number in 1990 (472), we can see that there is an increase in population from 1975 to 1990. Therefore, the answer is "No."

KarishmaB · Answer

Responding to a pm:
You don't need any calculations in this question. Just look at the data given and also on what is not given!

Question 3:

Species X pop of TY is constant from 1990 to 2005 so in 2005 also it will be about 970k. In 1990, it is about 2% of total mouse pop. We don't know what percent it will be in 2005 because we are not given that this percentage remains the same too. 
When Species X pop was about 950k in 1960, it was 3.3% of total pop. So in 2005, a similar figure could represent any percent of the total mouse pop.

So 2nd statement is supported:  The total mouse population of TY may not have remained roughly constant between 1990 and 2005. 
Since Species X could be any percent of total pop, the total pop could be any figure. So it may not have remained constant. 
 ANSWER

Look at the other statements:

TY most likely does not share a border with any other region in the study.

I do not know whether Species X moves from one region to another. The table gives me no indication. In fact, if anything, it shows that when the pop reduces, it reduces or stays steady in most regions. When it increases, it increases or stays steady in most regions. So there is no data to support anything about whether one region shares border with another region.

TY had the largest total mouse population of any region in the study in 2005.

No info about total mouse population in 2005 of any region. As we see, the percentages (Species X as a percent of total mouse pop) change with time so even if for some regions we know species X pop in 2005, we cannot say anything about total pop.

The total mouse population of EW grew more than twice as fast between 1990 and 2005 as the total mouse population of TY did.

As we discussed about, no info about total mouse pop in 2005.

TY was the only region in the study in which the Species X population remained relatively steady between 1990 and 2005.

No data to support this. It may have remained steady in IQ or JR or PS etc.

colfer · Answer

On the first table you have the numerator and second one gives you the fraction. Question stem is about total mouse population which is about the denominator. So depending on how the numerator (species X, first table) and the fraction ( bottom table) we need to work out the answers.

The total mouse population of TY changed more from 1960 to 1975 than from 1975 to 1990.  
numerator change is roughly the same between these years. % change is (3.4/.4=8) and (2/.4=5) between the years. Thus fraction decreases more in 60-75  than it increases in 75-90. Total population (denominator) must have decreased more in 60-75.

Rounded to the nearest million, the total mouse population of TY was 47 million in 1990. 
(968/2%)=47m

The total mouse population of TY fell from 1975 to 1990. 
numerator increases by (968/144)= 7 times whereas fraction increases by 5 times. Thus denominator should have increased. Total population couldnt have decrease because then the fraction will become greater than 7. In fact the population should have increased by 7/5=1.2 times roughly).

region's total mouse population exceeded 50 million in 1975 
IQ (1m=1%, 100% = 100m)
PS(162K=0.4% 250*162K=40.5m =100%)

shivanisomani02 · Answer

For Q.2

Two Conditions need to be satisfied :
1. Species X population decreased from 1960 to 1975
2. The region's total mouse population exceeded 50 million in 1975
 
Observe condition one for all three 
You can see that 
For JR there is an increase so no need to check condition 2.
 Ans: No 
For IQ and PS there is a decrease.

Condition 2
Total Population= (Species*100)/Percentage of total mouse population
Use Calculator
For IQ
Total Population in 1975 = 92834000/0.707=131,306,930 >50 Million 
 Ans: Yes 
For PS
Total Population in 1975=16204000/0.385=42,088,311<50 Million
 Ans: No

Sahil_Garg · Answer

Q2. or each of the following regions, select Yes if the region's Species X population decreased from 1960 to 1975 AND the region's total mouse population exceeded 50 million in 1975, Otherwise, select No,

To answer this question, we need to check two conditions for each region (IQ, JR, PS):
1. The region's Species X population decreased from 1960 to 1975.
2. The region's total mouse population exceeded 50 million in 1975.

Analysis:

1. *Region IQ:*
   - Species X population in 1960: 1,859,460
   - Species X population in 1975: 928,340
   - Decrease from 1960 to 1975: Yes
   - Total mouse population in 1975: To find the total mouse population in 1975, use the percentage data.
     - Percentage of Species X in 1975: 0.707%
     - Total mouse population in 1975: $ \frac{928,340}{0.707\%} \approx 131,294,911 $
   - Total mouse population > 50 million: Yes

Answer: *Yes*

2. *Region JR:*
   - Species X population in 1960: 21,900
   - Species X population in 1975: 24,590
   - Decrease from 1960 to 1975: No

Answer: *No*

3. *Region PS:*
   - Species X population in 1960: 219,670
   - Species X population in 1975: 162,040
   - Decrease from 1960 to 1975: Yes
   - Total mouse population in 1975: To find the total mouse population in 1975, use the percentage data.
     - Percentage of Species X in 1975: 0.385%
     - Total mouse population in 1975: $ \frac{162,040}{0.385\%} \approx 42,087,013 $
   - Total mouse population > 50 million: No

Answer: *No*

### Summary of Answers:

- IQ: *Yes*
- JR: *No*
- PS: *No*

chetan2u · Answer

Solutions for Q.1. and Q.2.

Q.1. For each of the following statements, select Yes if the statement is accurate based on the information in the passage and tables. Otherwise, select No.

As all three option depend on finding the total mouse population, let us use calculator and find the answer. 
1960:  Species X population was 947630, which is 3.356% of total, so total = 947360*100/3.356 =  28,228,844 
 1975:  Species X population was 144520, which is 0.351% of total, so total = 144520*100/0.351 =  41,173,790 
 1990:  Species X population was 968460, which is 2.051% of total, so total = 968460*100/2.051=  47,218,918

a. The total mouse population of TY changed more from 1960 to 1975 than from 1975 to 1990. 
  Yes ,  41 million from 28 million is larger than 47 million from 41 million.

b. Rounded to the nearest million, the total mouse population of TY was 47 million in 1990. 
  Yes ,  47, 218,918 is closest to 47,000,000, which is equal to 47 million.

c. The total mouse population of TY fell from 1975 to 1990.
 No ,  The population increased from 41 million to 47 million.

Q.2. For each of the following regions, select Yes if the region's Species X population decreased from 1960 to 1975 AND the region's total mouse population exceeded 50 million in 1975, Otherwise, select No,

It would be best to check for decrease and then for 50 million.

Decrease in species X population:  A quick glance at the table tells us that IQ and PS had species X population decreasing, while NR had more species X rats in 1975.

Thus, we check for the total population in IQ and PS in 1975.
IQ:  Species X population was 928340, which is 0.707% of total. Clearly, the total > 100 million so total = 928340*100/0.707= 131,306,931 > 50 million
 PS:  Species X population was 162040, which is 0.385% of total, so total = 162040*100/0.385= 42,088,312 < 50 million

Answer:  Yes for IQ and No for remaining two.

Gemmie · Answer

1. For each of the following statements, select Yes if the statement is accurate based on the information in the passage and tables. Otherwise, select No.

The total mouse population of TY changed more from 1960 to 1975 than from 1975 to 1990. => Yes

TY's total mouse population

+ 1960:  \frac{974*10^3}{3.356} * 10^2 = 282 * 10^5

+ 1975:  \frac{144}{0.351} = 410  (skipping the 10^5 part)

+ 1990:  \frac{968}{2.051} = 471  (skipping the 10^5 part)

From 1960 to 1975: increase by more than 100
From 1975 to 1990: increase by less than 100

Rounded to the nearest million, the total mouse population of TY was 47 million in 1990. => Yes

As calculated above, TY's total mouse population in 1990 is  471 * 10^5 = 47.1 * 10^6

The total mouse population of TY fell from 1975 to 1990. => No

As calculated above, TY's total mouse population increased from 1975 to 1990

2. For each of the following regions, select Yes if the region's Species X population decreased from 1960 to 1975 AND the region's total mouse population exceeded 50 million in 1975, Otherwise, select No.

Requirement:
+ Species X population decreased from 1960 to 1975
+ Total mouse population in 1975 > 50 * 10^6

IQ => Yes 
+ Species X population decreased from 1.8m -> 928k
+ Total mouse population in 1975:  \frac{465*10^3}{0.262} * 100 = 1774 * 10^5 = 177 * 10^6

JR => No 
+ Species X population increased from 1960 to 1975

PS => No 
+ Species X population decreased from 219k to 162k
+ Total mouse population in 1975:  \frac{162*10^3}{0.385}*100 = 420 * 10^5 = 42 * 10^6

3. Assume that the Species X population totals of TY remained roughly constant between 1990 and 2005. Which one of the following statements is best supported by the information provided? 
 The total mouse population of TY may not have remained roughly constant between 1990 and 2005.

Might be, because from the provided data, it seems that the ratio of Species X to the Total mouse population varies from time to time.

Therefore, even if Species X population totals of TY remained roughly constant between 1990 and 2005, the ratio of Species X to the Total mouse population might change significantly, making the Total mouse population change significantly accordingly.

Regarding other choices, cannot find any data supporting them

user1937 · Answer

How are supposed to do the calculation for second part? Approximating it one would assume 960,000 and 2% and arrive at 960,000/0.02 =48 million approx, and would mark 47 million as incorrect. Is there a trick to follow for such questions?

bb · Answer

You would use the built-in calculator.... if you have to.

ashishzzzzz · Answer

GMATNinja   MartyMurray

Please help me understand question 3.
I encountered this question in my mock and it was very difficult for me to understand!

GMATNinja · Answer

Question 3

Q3 asks us to imagine that the Species X population totals in TY stay constant between 1990 and 2015, so let's start there. In 1990, the population total of TY was 968,460, so we'll assume the same figure for 2015.

Next, let's go to the "Data Tables" tab to see what else we can learn about TY. According to the second table, in TY, the population of Species X as a percentage of the total population bounces around pretty wildly. It's over 3% of the population in 1960, about .3% in 1975, and then 2% in 1990.

Now, let's evaluate the answer choices one by one.

That seems like a throwaway answer. How can we assume anything about the geography of TY based on the population trends of Species X? Eliminate.

Interesting. First, the language. "May not have," is a pretty low bar to clear -- it just means there's a possibility that something is true.

Second, recall what we noted about Species X as a percentage of the total population, historically. It bounces around a bunch, meaning that the population of Species X doesn't offer much insight about the total population trends -- if it did, those percentages would be pretty stable.

If the total population doesn't move the way the population of Species X moves, well, it stands to reason that just because the population of Species X didn't change doesn't mean that the total population in TY didn't change. It  may have  changed.

So let's hang on to (B).

Nah. We know close to nothing about what happened to the total mouse population in TY, let alone what happened in other regions.

Put another way, having limited info about the changes in the population of Species X gives us close to nothing about trends for total populations.

Similar problem here. All we know about EW is that the population of Species X plummeted by 52% during this time. That tells us little about total population trends, but if anything, you'd imagine the total population of EW might also be decreasing. Kill (D).

Well, we know that the population of Species X changes in EW and in CV, but we know nothing about the populations of PS, JR, or IQ during this time. Entirely possible that the Species X populations remained stable. We don't know.

Looks like (B) is the best of the bunch.

I hope that helps!

Sa800 · Answer

someone please solve question one...why are people in the above answers not using the full ~947,000 number...? To get total population shouldnt you write an equation like this

947630 = (3.356/100) * X

and X is the total mouse population?

KarishmaB · Answer

People are estimating to save time since it is such a big number. The same estimation is used on all parts so the results are comparable. Ignore the last 3 digits of LHS and 100 from RHS

Directly calculate 948/3.356 to get an approximate value without following zeroes. 
You will get X = 28236889
With their shorthand, they are getting 282 (the first 3 digits only) and comparing these with the first 3 digits in other cases too hence saving a lot of time.

Aishna1034 · Answer

Can you please post explanations for questions 1,2 as well?

Bunuel · Answer

Please read the whole thread: https://gmatclub.com/forum/researchers- ... l#p3403443

Researchers studying long-term changes in regional mouse populations h

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	TY most likely does not share a border with any other region in the study.
	The total mouse population of TY may not have remained roughly constant between 1990 and 2005.
	TY had the largest total mouse population of any region in the study in 2005.
	The total mouse population of EW grew more than twice as fast between 1990 and 2005 as the total mouse population of TY did.
	TY was the only region in the study in which the Species X population remained relatively steady between 1990 and 2005.

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Researchers studying long-term changes in regional mouse populations h

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