Researchers studying long-term changes in regional mouse populations h

OA for 1

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.­

Can someone please reply to the 2nd question.

Please explain q1 part a and q3

­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

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?

correct me if I am wrong: the qs is asking for 3 towns in which the population of species X has decreased from 1960 to 1975 and also in each town the TOTAL POPULATION OF mouse in 1975 was more than 50 million.

1. IQ we can see from the top chart that it decreased from 1,859,460 to 928,340, and also we see that 928,340 in 1975 represented 0,707% from the TOTAL POPULATION OF MOUSE, so 928,340. x =0,707/100 (928,340 of x representing the total population) give us 0,707 of the total population, isolating x we get 132,857,142 > 50.000.000 so, yes IQ decreased from 1,859,460 to 928,340 in species X and is greater than 50 million in 1975.
2. we see that in JR the popu of species X does increase, so we do not have to calculate the total population and we have a no.
3. in PS there is a decrease and if we calculate the total population we get : 162,040 x = 0.385/100 = 42,105,263, which is no more than 50 million so we get a no answer

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

wow i went 3 for 3 on this one!!!! hit me up if anybody has any questions.

GMATNinja MartyMurray

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

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!

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?

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.