Detangle the argument in your own words:

There are CURRENTLY 45% of fast-food restaurants in Cantaria that normally cater to young people.
The author then concludes that because average age of the population is rising, THERE WILL be fewer of these restaurants.

The author is making a prediction about the future. Most importantly, he assumes NOTHING else is changing between now and then. i.e. The population of young people is NOT increasing.
That is what answer choice C highlights. This type of assumption regarding predictions is very typical in CR - pay attention.

Fast-food restaurants make up 45 percent of all restaurants in Cantaria. Customers at these restaurants tend to be young; in fact, studies have shown that the older people get, the less likely they are to eat in fast-food restaurants. Since the average age of the Canatrian population is gradually rising and will continue to do so, the number of fast-food restaurants is likely to decrease.

Which of the following, if true, most seriously weakens the argument?

(A) Fast-food restaurants in Canatria are getting bigger, so each one can serve more customers. (It means the number is not decreasing so its wrong)

(B) Some older people eat at fast-food restaurants more frequently than the average young person. (Its breaking our argument)

(C) Many people who rarely eat in fast-food restaurants nevertheless eat regularly in restaurants. ( not our concern ) wrong

(D) The overall population of Canatria is growing steadily. (Yes correct)

(E) As the population of Canatria gets older, more people are eating at home.( Thats not our concern, Are they eating at fast food restaurant or not. That is our concern( Wrong)

Fast-food restaurants make up 45 percent of all restaurants in Cantaria. Customers at these restaurants tend to be young; in fact, studies have shown that the older people get, the less likely they are to eat in fast-food restaurants. Since the average age of the Canatrian population is gradually rising and will continue to do so, the number of fast-food restaurants is likely to decrease.

Which of the following, if true, most seriously weakens the argument?

Argument = Older people eat less at fast food restaurants + Avg Canatria age increasing -> # fast food goes down

(A) Fast-food restaurants in Canatria are getting bigger, so each one can serve more customers. out of scope; if anything this strengthens conclusion (more ppl can fit in a restaurant, less restaurants are needed )

(B) Some older people eat at fast-food restaurants more frequently than the average young person. this one is tricky! makes it seem like bc there's older people that eat at restaurants more frequently than the avg young person, it contradicts a premise BUT you have to remember this doesn't mean that the AVG old person doesn't eat as frequently as the AVG young person, just like there can be genius high schoolers smarter than the avg college student but it doesn't mean the avg high school student is smarter than the avg college student

(C) Many people who rarely eat in fast-food restaurants nevertheless eat regularly in restaurants. out of scope

(D) The overall population of Canatria is growing steadily. even if the avg age goes down, if there's same or more young people than the amt of restaurants may not go down

(E) As the population of Canatria gets older, more people are eating at home. wrong, if anything this strengthens. more old people eating at home -> less fast food restaurants

VeritasKarishma

if in option b All is mentioned instead of some will then optin is correct

like in this question it's not 100 % full proof weaken ans
i have seen many questions like the same which aren't 100% proof ans in strenthen and weaken type. So should i look for options which just provide belief of either strengthening or weakening

Any other insights you wants to give regarding this type of answers

If (B) has "all" in place of "some", it will negate this premise:
"studies have shown that the older people get, the less likely they are to eat in fast-food restaurants"

We need to take the premises to be true. It doesn't make sense then to have its negation true too.
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When can the average age of a population rise and continues to rise?
Few possibilities are:
- When there are no deaths at older ages and no new born babies - Steady population
- When the number of people moving to old age is greater than the number of newly born - Growing population
- When the population comprises of only young people and nobody dies - Steady population
- When the number of newly born are more than the total age of people growing older/total age of people dying - Growing population

The assumption in the question is that the just because the average age of the population is rising, there would be only older people in the population as a whole. We can see that the author has ignored other possible scenarios.

Which of the following, if true, most seriously weakens the argument?

(A) Fast-food restaurants in Canatria are getting bigger, so each one can serve more customers. - The reason for decrease in fast-food restaurant is attributed to the fact that there would be older people in the population. The fact that fast food restaurants in Canatria are getting bigger and can serve more customers has no impact on the conclusion. A definite Loser!

(B) Some older people eat at fast-food restaurants more frequently than the average young person - The eating pattern/frequency of older people is introducing another variable in the analysis. The variable we need to analyze are 'average increase in the population' resulting to 'decrease in the fast food restaurants' - Loser

(C) Many people who rarely eat in fast-food restaurants nevertheless eat regularly in restaurants - Many people? Who are these people? How does the fact that they rarely eat in fast-food restaurants while eat regularly in restaurants affect the author's reasoning around that the average age increase would result in decrease in fast-food restaurants in the future? It does not! Loser

(D) The overall population of Canatria is growing steadily - If we consider the last case mentioned above, then the growing population is actually resulting in more new borns, thus more young people in the times to come. It does give us a reason to doubt the relationship between the average age rise and the decrease in the fast-food restaurants - Contender and Winner

(E) As the population of Canatria gets older, more people are eating at home - No relation to the argument!

A few Kudos would help
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