People who are red/green color-blind cannot distinguish between green and brown. Gerald cannot distinguish between gr...
ReinaNovember 1, 2019
S&N Question #2 on koala and deforestation
I am confused on how to diagram the two parts/speakers to be able to compare them. What is the correct way to diagram this to get to one of the answer choices?
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@Reina Happy to help! This is a difficult question.
*Note that this is an explanation for the 2nd question in the Sufficient & Necessary Questions Lesson regarding deforestation and koalas. It is not for the red/green color-blind question although it may appear on the message board connected to that question.
The biologist says, "IF the forest continues to disappear at its present pace, [THEN] the koala will approach extinction." This claim can be diagrammed as: FD -> KE. The contrapositive of this is not KE -> not FD.
The politician says,"So all that is needed to save the koala is to stop deforestation." This is diagrammed as: not FD -> not KE. The contrapositive of this is KE -> FD.
Therefore, the biologist and the politician are saying two different things.
Biologist: FD -> KE not KE-> not FD
Politician: not FD -> not KE KE -> FD
We are looking for an answer that is in line with the biologist's claim, but not the politician's. (B) "Deforestation is stopped and the koala becomes extinct" achieves this. The biologist never places "KE" nor "not FD" as the Sufficient condition, so (B) does not affect that claim/is consistent with it. However, (B) is inconsistent with the politician's claim, because if deforestation was stopped (not FD) it would follow that the koalas should not become extinct (not KE). Similarly, the koalas were to become extinct (KE), it would follow that the forest would disappear (FD). However, (B) has both the forest not disappearing and the koalas becoming extinct occuring. So, (B) is correct.
Does this make sense? Please let us know if you have additional questions!
ReinaNovember 5, 2019
Why does it making "KE" and "not FD" the sufficient condition make it correct? I understand where you are getting those from but I don't understand how they fit with the principal statement and the contrapositive to make that the right answer
SkylarNovember 16, 2019
@Reina,
We broke down the arguments as follows.
Biologist: FD -> KE not KE -> not FD
Politician: not FD -> not KE KE -> FD
Answer choice (B) gives us the variables "not FD" and "KE."
With these in mind, we refer back to the biologist's and politician's arguments to see if we can make any deductions from these two given variables. In order to make a deduction, we need "not FD" or "KE" to be a sufficient condition, so that we can conclude a new necessary condition.
The biologist has neither of these two variables as a sufficient condition. Therefore,the biologist does not make any claims about what will happen given the scenario in (B), meaning it could be true. So, answer choice (B) is consistent with the biologist's argument.
However, the politician's argument takes the variable "not FD" as presented in (B) as a sufficient condition to conclude "not KE." We cannot have "not KE" because the other variable (B) gives us is "KE." Since these two conditions oppose each other, (B) has to be inconsistent with the politician's claim. [Note that the same thing would happen if we started with the second variable given in (B) - "KE" - and concluded "FD" which opposes "not FD."]
