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Over the last 10 years, there has been a dramatic increase in the

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New post 13 Sep 2018, 08:35
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Question Stats:

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Over the last 10 years, there has been a dramatic increase in the number of people over the age of 65 living in this region. This is evident from the fact that during this time the average age of people living in this region has increased from approximately 52 to 57 years.

Which one of the following, if true, would most strengthen the argument?

(A) The number of people in the region under the age of 18 has increased over the last 10 years.
(B) The birth rate for the region decreased significantly over the last 10 years.
(C) The total number of people living in the region has decreased over the last 10 years.
(D) The number of people who moved into the region over the last 10 years is greater than the number of those who moved out.
(E) The average age for people in the region is higher than that for people in the surrounding regions.

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New post 13 Sep 2018, 09:27
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Over the last 10 years, there has been a dramatic increase in the number of people over the age of 65 living in this region. This is evident from the fact that during this time the average age of people living in this region has increased from approximately 52 to 57 years.

Which one of the following, if true, would most strengthen the argument?

(A) The number of people in the region under the age of 18 has increased over the last 10 years.
other factors being constant. This is will increase the overall average. Keep It.

(B) The birth rate for the region decreased significantly over the last 10 years.
Not exactly helpful, we need to have mortality rate also if we need to compare it. Drop it.

(C) The total number of people living in the region has decreased over the last 10 years.
Not unless we know the age of people leaving the region. Drop it.

(D) The number of people who moved into the region over the last 10 years is greater than the number of those who moved out.
Same as C, we can not infer anything unless we know the age. Drop it.

(E) The average age for people in the region is higher than that for people in the surrounding regions.
Irrelevant. Drop it.

Answer: A
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Re: Over the last 10 years, there has been a dramatic increase in the  [#permalink]

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New post 13 Sep 2018, 09:55
can somebody please explain the OA?

As per Average concept, if a sample with n elements have average X and for a n+1 element to come and increase the average of the sample, the (n+1)th element need to have value greater than sample average i.e X.

How come increasing the number of people under age 18 increases the average from 52 to 57?

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New post 13 Sep 2018, 11:13
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Hello Subhashish

I'll try to help
we have to strengthen the fact that the number of people over 65 have increased.
Now, how can we increase the average. you are write with your approach. whenever something greater than the average is added to the set.

Now consider this,
we add a figure to a set that is actually less than the average.
Average is going to decrease.
but what if we have to increase the average ?
we will first have to add the relevant amount( equal to the amount less than the average to bring it back to the normal) and then increase it some more.

Answer choice A does exactly just that: its says that the no of people below 18 has decreased. but we already know that the overall average has increased. thus there must be some addition of a figure that is greater than the average to increase the average.

However this choice will make sure that the no of people over 55 has increased, but it can not guarantee that the no of people over 65 has increased.
but if you will look at the other answer choices, they have graver loopholes in them.

Hope this helps.
Shubhasish wrote:
can somebody please explain the OA?

As per Average concept, if a sample with n elements have average X and for a n+1 element to come and increase the average of the sample, the (n+1)th element need to have value greater than sample average i.e X.

How come increasing the number of people under age 18 increases the average from 52 to 57?

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Re: Over the last 10 years, there has been a dramatic increase in the  [#permalink]

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New post 13 Sep 2018, 14:19
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Quote:
Answer choice A does exactly just that: its says that the no of people below 18 has decreased.


Are you sure?
OA should be (B).


A:
Quote:
(A) The number of people in the region under the age of 18 has increased over the last 10 years.

result: more infants were born; as a result, the average age of people living (probably) drops.
B:
Quote:
(B) The birth rate for the region decreased significantly over the last 10 years.

result: birth rate decreased; the population continues to age.
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New post 13 Sep 2018, 15:17
Kaczet wrote:
Quote:
Answer choice A does exactly just that: its says that the no of people below 18 has decreased.


Are you sure?
OA should be (B).


A:
Quote:
(A) The number of people in the region under the age of 18 has increased over the last 10 years.

result: more infants were born; as a result, the average age of people living (probably) drops.
B:
Quote:
(B) The birth rate for the region decreased significantly over the last 10 years.

result: birth rate decreased; the population continues to age.


OA should not be (B). OA is (A) as stated
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New post 13 Sep 2018, 16:03
I don't understand why it is A. In Q stem, average is increasing and according to option A, we are adding more people of age far below the average. How average can increase.!

Something is wrong with this question.
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New post 13 Sep 2018, 16:04
nightblade354, elaborate on the answer, pls.

Thanks.
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New post 13 Sep 2018, 19:11
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Kaczet,i’ll do my best to let u understand why A is the answer and not B(since u’ve said B should be the answer)

Conclusion = “the number of people with age over 65 yrs has increased DRAMATICALLY”

Premise = “the average age has increased from 52 to 57”.The premises are facts that need to be taken as hard truths.

A-The number of people under 18 has increased = implies that the number of people older 52 has to increase(because the average has increased)

Now how does this strenthen the conclusion that 65+ increased..?

The difference between (52 and 18) is bigger than (52 and 65).So if the average increased from 52 to 57 the number bigger than 65 has to even bigger because the number below 18 has increased.

B-If the birth rate has come down,it strengthens the fact that the number of 65+ People also should have come down.

Consider this= previously when the birth rate was high(consider their age to be 0 or 1).to even this out(because avg has increased from 52 to 57), the people with 65+ Should have gone up for sure.Now since the number of births has come down,the number of 65+ need not necessarily increase.

Phew!!!excuse me for the long explanation.

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New post 13 Sep 2018, 19:15
This was one of those questions where I wouldn’t have to even read the other options to say A is the answer.A just hit the nail on the head.

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New post 14 Sep 2018, 04:21
Here is an explanation from the LSAT arm of MGMAT: https://www.manhattanprep.com/lsat/foru ... -t803.html

This one has boggled people ever since it appeared on that test. I think the most difficult part is how counter intuitive it is and how it plays off another logical reasoning question type. If we were trying to explain why average age increased, an answer choice like (B) would be very tempting. Answer choice (B) states that the birth rate has decreased over the past 10 years. If there are less babies around, people usually say to themselves, "that's why the average age increased! This has got to be the answer."

However, our goal is not to explain a result, but rather strengthen the conclusion. We know the average age increased from 52 to 57. There are two obvious explanations for why the average age would increase. First, that the number of older people (over 65) has increased. Or second, that the number of younger people decreased. The argument concludes that it's the first of these two options. However, the argument failed to consider that it was the latter option. To support the conclusion, let's reinforce the notion that its the first option by challenging the possibility that it's the second option.

Another way to see this would be

If there were only two ways to get to school, ride the bus or walk. If I want to support the idea that you walked to school today I could undermine the idea that you took the bus. Just by saying that you did not take the bus, I have supported the idea that you walked to school.

So, in this example. To support the idea that we have more old people, I want to say that it is not the case that we have less young people. By saying that we have more young people, I make it all the more likely that there are more old people. Otherwise, why did the average age go up? Answer choice (A) says that it's not for a decrease in young people that the average age went up. Answer choice (A) eliminates an alternative explanation.

(A) is correct for the reasons above.
(B) weakens the argument by supporting an alternative explanation for why the average age went up.
(C) doesn't tell us about the average age of those people. Who cares that there are more of them, I need to know how old they are!
(D) is irrelevant. Same problem as answer choice (C).
(E) is irrelevant. The argument is not a comparison between this region and surrounding regions, but rather a comparison of this region at one point in time with the same region at another point in time.

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

So here's the argument in a nutshell:

The average age increased from 52 to 57.

Therefore, there has been a dramatic increase in the number of people over the age of 65.

Is that logical? Aren't there other things that could be responsible for the change in average age?

(A) states that the number of really young people has increased. This would make it hard to increase the average age so much. With this in mind, the conclusion now makes more sense -- it now seems more feasible that more really old people moved to the area, compensating for the big increase in average age.

(B) does exactly the opposite. It states that there are fewer infants around to weight down the average age. That alone could be enough to cause the increase in average age. This is a classic weaken answer choice because it offers an additional potential cause for the result cited (increase in average age).

Seeing it clearly as a causal argument really helps. Know what I mean?

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
This can do a far better job explaining this question than I could. With respect to everyone who has gotten this wrong, please know that even MGMAT concedes that this has been bringing down LSAT scores since its inception.
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New post 14 Sep 2018, 07:10
nightblade354 wrote:
Over the last 10 years, there has been a dramatic increase in the number of people over the age of 65 living in this region. This is evident from the fact that during this time the average age of people living in this region has increased from approximately 52 to 57 years.

Which one of the following, if true, would most strengthen the argument?

(A) The number of people in the region under the age of 18 has increased over the last 10 years.
(B) The birth rate for the region decreased significantly over the last 10 years.
(C) The total number of people living in the region has decreased over the last 10 years.
(D) The number of people who moved into the region over the last 10 years is greater than the number of those who moved out.
(E) The average age for people in the region is higher than that for people in the surrounding regions.


This is a great question.

As per premise:
Cause: Over the last 10 years, the average age of people living in this region has increased from approximately 52 to 57 years.
Effect: there has been a dramatic increase in the number of people over the age of 65 living in this region.

---younger group------Average ------elder group---

The conclusion is strengthened if we can show that age group of over 65 has contributed to the increase in average age from 52 to 57 years, and this is bolstered if the other age group on the left side of average (the younger group) has not pulled the average down.
A indicates just that.
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New post 14 Sep 2018, 12:41
I chose B, but now understand why A is the answer.

For B, if birth rate went down and there is less babies than 10 years ago, this means the average could have just gone up from 52 to 57 if people in other age groups have just aged and increased the average age.

However, for A, teenagers grew steadily, then there must have been a higher increase in the older groups to increase the average age from 52 to 57, therefore strengthening the argument .
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