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CR Questions (solar energy, deer tick, animal allergy)

Hi Zeyu! May I seek some help/direction on how to solve these questions? I don’t have clue even after knowing the answer

Q82 Technological improvements and reduced equipment costs have made converting solar energy directly into electricity far more cost-efficient in the last decade. However, the threshold of economic viability for solar power (that is, the price per barrel to which oil would have to rise in order for new solar power plants to be more economical than new oil-fired power plants) is unchanged at thirty-five dollars.
Which of the following, if true, does most to help explain why the increased cost-efficiency of solar power has not decreased its threshold of economic viability?
A. The cost of oil has fallen dramatically.
B. The reduction in the cost of solar-power equipment has occurred despite increased raw material costs for that equipment.
C. Technological changes have increased the efficiency of oil-fired power plants.
D. Most electricity is generated by coal-fired or nuclear, rather than oil-fired, power plants.
E. When the price of oil increases, reserves of oil not previously worth exploiting become economically viable.
(Ans: C)
I wonder what is the difference between options A & C?

Q100 Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.
Which of the following would it be most important to ascertain in evaluating the argument?
A. Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white-footed mice
B. Whether the size of the deer tick population is currently limited by the availability of animals for the tick’s larval stage to feed on
C. Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice
D. Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed
E. Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans
(Ans: B)

Q#) People who have spent a lot of time in contact with animals often develop animal-induced allergies, some of them quite serious. In a survey of current employees in major zoos, about 30 percent had animal-induced allergies. Based on this sample, experts conclude that among members of the general population who have spent a similarly large amount of time in close contact with animals, the percentage with animal-induced allergies is not 30 percent but substantially more.
Which of the following, if true, provides the strongest grounds for the experts’ conclusion?
A. A zoo employee who develops a serious animal-induced allergy is very likely to switch to some other occupation.
B. A zoo employee is more likely than a person in the general population to keep one or more animal pets at home
C. The percentage of the general population whose level of exposure to animals matches that of a zoo employee is quite small.
D. Exposure to domestic pets is, on the whole, less likely to cause animal induced allergy than exposure to many of the animals kept in zoos.
E. Zoo employees seldom wear protective gear when they handle animals in their care.
(Ans: A)
I have problem understanding why the allergy rate is 30% or more of the exposed members of general population (group A), isn’t it saying 30% is of the employees in zoos (group B). I suppose they are not the same groups?

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Wow… Great questions. I am happy you raise these tough ones, each of them at least 750 level!

Q1. The key thing is to understand properly the concept of “threshold”. Let us use our strategy 1 in math to translate it into the mathematical language:

Before:
Cost A$, say 55$ of costs of equipment to produce 1 unit of electricity
Cost B$ (say $40) = C$ (oil price, say 20$ ) + D$ (oil equipment, 20$) to produce 1 unit of electricity

So the oil price need to rise to 35$ so that 35$ + 20$ = 55$= A -> for solar power plants to be viable

Now:
Cost 45$ for solar to produce 1 unit of electricity (cost-efficiency has improved)
Cost B$’ = C’$ + D’$ to produce 1 unit of electricity

What we know as a fact is the threshold is still 35$, i.e. in translation: 35+D=45 <=> D = 15$ <=> cost-efficiency for oil has improved.

Therefore you see after translation, it has nothing to do with oil price. The threshold is the price calculated such that the cost of solar plant per unit of electricity = cost of oil plant per unit of electricity

Q2. I guess you have an inclination to choose D
First you should understand the line of reasoning of the author:

Fact 1: cause (bacterium by deer ticks) -> effect (Lyme disease)
Fact 2: cause (deer tick larvae feed on white-footed mice) -> effect (bacterium by deer ticks)

Reasoning:
Premise 1: certain other species the larvae feed do not have the bacterium
Premise 2: Population of these “other species” increase
Conclusion 1: more larvae would be feeding on uninfected hosts -> conclusion 2: Number of infected deer ticks decrease

This is a causal relationship from cause to effect.
As I always emphasized in the class - for causal relationship from cause to effect, except for the 3 properties of causal relationship, ask yourself - it depends on what?

The formula works the following:
Number of deer ticks (N) * Proportion of infection ( P ) = Number of deer ticks infected by the bacterium (X)

The author’s reasoning means:
Population of these “other species” increase -> P decreases -> X decreases, but he forgets N

What “B is true” means is that the population of “other species” + population of “white-footed mice” -> determines N
So, Population of these “other species” increase -> P decreases but N increases -> X may not decrease: this is exactly “other factors tend to make the conclusion not happen” (C->Not B - weakening)

If “B is false”, then N has nothing to do with other species’ population, therefore the author’s reasoning is strengthened.

This analysis also shows that “D” is fighting against the fact 2 - you should NOT fight against the fact, you should only fight against the author’s reasoning

Q3:
Author’s reasoning:
fact: 30% zoo employees have animal induced allergies

conclusion: for normal people who have similar amount of contact, much more than 30% have animal induced allergies

“B”“C” is irrelevant, “D” is weakening, “E” is more close to “weakening”

Let me explain why “A” - in probability world, we call this "survivorship bias"
As many those who got the allergies switch to other jobs, the remainings are the "survivors"
Let us see totally zoo employee = N = A (those who stay) + B (those who switch)
Those who stay has 30% chance for allergies and those who switch have close to 100% chance for allergies (that is the main reason they switch)
So totally, we have A * 30% + B * 100% = 0.3A + B have allergies
So the real infection rate = (0.3A + B) / (A+B) = (0.3A+ 0.3B + 0.7B)/ (A+ B) = 30% + 70%B/N > 30%

Q1 and Q3 are mathematical reasoning - a type I did not mention in our CR class. I will add these two examples into our future CR handout.

How to solve them, as you can see from these examples - our 3 strategies in math session applies -> translation

Thank you so much, Zeyu! The answers are very helpful.

For Q1: I have totally ignored that the cost of C can be composed of several items.
For Q2: D was not my option as I could not choose any options. I ignored B at the very beginning as I thought if it was true, the effect would be uncertain. I was not aware of if it is wrong.
For Q3: good explanation!