Logical reasoning PrepTest 119 · Section 3 · Question 22

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
The average age has gone up from 52 to 57, so there must be more people over 65 living here.

Answer Anticipation:
Whenever an argument is talking about the number of people and the average, you should start to think that it might just be committing a Percent vs. Amount flaw.

Here, the argument uses the average age increasing to suggest that the population of those over 65 also went up. However, what it actually supports is that the percentage of the population over 57 increased. That doesn't necessarily mean the number of people over 65 went up. It could be that there was a mass exodus of young people from the area (maybe a large college shut down).

In order to support an increase in the number of people over 65, it would have to be shown that the total population increased dramatically, or the people under the age group in question increased thus requiring an increase in the elderly to allow for the increased average age. So to strengthen the argument, let's find an answer to that effect.

Answer Explanation:
If the number of people under the age of 18 has increased but the average age has gone up by 5 years, then it's almost certain that the number of people at the upper end of the age band must have gone up as well in order to drag that average up. In fact, by focusing on those well under the average age, it makes it more likely that those well over it increased in population, and that the increase was substantial. (After all, there isn't much room above 57, since people don't live forever.)

Key Takeaway:
While calculating an average requires knowing the total amount being averaged, knowing the average doesn't tell you anything about that total. It's a similar jump as the one from percentage to amount.

Incorrect. This answer suggests another possibility—the number of people over 65 stayed the same, but the number of people under 10 has gone down, bringing the average up.

Incorrect. If the total number of people went down, then the average age could go up despite the elderly population decreasing if they moved out of the area at a lower rate than the younger folk.

Incorrect. So close! This answer does establish that the population increased, but we need an answer that supports the conclusion that the increase in those over 65 is dramatic. If there was a slight increase in population but a shift of people in their 20s moving out and their early 60s moving in, then the average age could increase without a single additional 65+ year old person in the area.

Incorrect. What's happening in other regions doesn't speak to population growth in this one.