Critical Reasoning

"Life expectancy" is the average age at death of the entire live-born population. In the middle of the nineteenth century, life expectancy in North America was 40 years, whereas now it is nearly 80 years. Thus, in those days, people must have been considered old at age that we now consider the prime of life.

Which of the following, if true, undermines the argument above?

a. In the middle of the nineteenth century, the population of North America was significantly smaller than is today.

b. Most of the gains in life expectancy in the last 150 years have come from reductions in the number of infants who die in their first year of life.

c. Many of the people who live to an advanced age today do so only because of medical technology that was unknown in the nineteenth century.

d. the proportion of people who die in their seventies is significantly smaller today than is the proportion of people who die in their eighties.

e. More people in the middle of the nineteenth century engaged regularly in vigorous physical activity than do so today.

Answer is B

Answer is indeed B, But i am not able to rule out A. I don't know what I am missing. Can anyone please explain choice A with the help of an example or in detail.

Will really appreciate your replies. This choice has stuck me.

Thanks & Regards
Sachin

Hint: average vs numbers

nileshdalvi wrote:Hint: average vs numbers

nileshdalvi, thanks for the hint.

As per your hint, argument talks about life expectancy that is the average age, and choice (A) talks about population of North America.

I am not sure, but it looks more like a strengthener to me.
Suppose, population of North America earlier = 200
population of North America today = 2000

People earlier were considered old at 40
People now are considered old at 80

This extension of life expectancy (40 to 80) has also affect the population. If people were dying earlier at the age of 40, then their life was short as compared to now.

Conclusion is :- Thus, in those days, people must have been considered old at age that we now consider the prime of life.

Age 40 is now considered prime of life, which means people don't die earlier. They are part of the population.

I think this choice as a strengthener, but I am not sure.

Experts please help me.

Regards
Sachin

sachin_yadav, I could not somehow understand this statement quoted by you
"This extension of life expectancy (40 to 80) has also affect the population. If people were dying earlier at the age of 40, then their life was short as compared to now. "

Using a similar HYPOTHETICAL example,which satisfies A

Suppose, population of North America earlier = 2
population of North America today = 4

and individual statistics as 20,40 and 100,80,80,60 respectively.

IMO, even if this was reverse, we could have had the populations as 100,60 and 20,40,60,40 and this would have kept the average same. So, population in either case does not affect the average at all.

So it neither strengthens not weakens.

Not sure if I have answered your specific question, please elaborate in case needed.

I received a PM on this one...

This is Critical Reasoning question 1 in the 12th edition.

Sachin - what is going on here might be a premise - conclusion type of confusion.

You say "This extension of life expectancy (40 to 80) has also affected the population. If people were dying earlier at the age of 40, then their life was short as compared to now."

What we really need to focus on first, before anything else, is sorting the premises and conclusions out and finding the structure of this argument.

Start with the conclusion. "Thus" provides you with a good clue here...

conclusion is "Thus, in those days, people must have been considered old at age that we now consider the prime of life."

What is the evidence for this (the premise)? The premise is "In the middle of the nineteenth century, life expectancy in North America was 40 years, whereas now it is nearly 80 years."

So this is what we are saying -- because life expectancy is now 80 years when it was 40 in the past, the people who would have been thought really old in the past are now in the prime of their life.

You see that B is the correct answer because the average age can be heavily influenced by outliers. In terms of age there is no bigger outlier than infants who die in the first year of life. One infant and one 80-year old would have a life expectancy of just 40 years. So perhaps just as many people lived to 80 in the past, yet many died as infants. So choice B is great.

Your question was about Choice A. Choice A does not actually strengthen or weaken. We are talking about the life expectancy not the number of people. Brazil has a much larger population that Switzerland, but Switzerland has a much higher life expectancy. Remember the direction that we are going here. The answer choice would need to weaken the conclusion. So the fact that there were fewer people in North America 150 years ago would need to weaken the conclusion that old age then is prime of life now. But there is no connection in that direction. I do see what you mean that people living longer would result in a larger population -- but that is the wrong direction. You are not trying to prove or disprove that the population was larger you are trying to prove or disprove that old then is prime of life today and the number of people in North America neither strengthens nor weakens the life expectancy.

I hope that I have correctly understood what your question was!

Thanks David and nileshdalvi

David, this is exactly what I was thinking about (A). Thanks for clearing my doubt.

Regards
Sachin

Mathematical and logical answer is (B)

Conclusion is about AGE, 'A' doesn't talk about it.

Eliminate A !

Can anyone plz tell me why option C was wrong ?

Choice C "Many of the people who live to an advanced age today do so only because of medical technology that was unknown in the nineteenth century."

This does not impact the argument.

The conclusion of the argument is that what is now considered "prime of life" was considered "old" in the nineteenth century.

The evidence is that of average life expectancy - 40 years then compared to 80 years now.

We want to weaken the conclusion. Just saying HOW people live longer now does not weaken the idea that people are older these days. Right? So what if they use medical technology, they still live longer!

Does that help?