The video is not invoking the necessary condition to conclude the sufficient condition.
The video is showing that the necessary conditions of the principle rule and its contrapositive always create a possible scenario.
In this case, the two necessary conditions of the biologist are: "KAE" and "not FCD," so: the Koala can become extinct even if deforestation stops.
However, the politicians necessary conditions are: "not KAE" and "D," so: the Koala can be saved even if deforestation continues.
Answer choice (B) states that deforestation is stopped and the koala becomes extinct.
As we explained above, the necessary conditions of the biologist show that this can be possible. However, the politician tells us that if deforestation is stopped, then the koala does not approach extinction.
Thus, answer choice (B) is consistent with the biologist's claims, but not with the politician's.
Hope that clears things up! Please let us know if you have any other questions.
dallman0303August 4, 2015
This does help thank you! Could you point me to the lesson that demonstrates the utilization of both the Necessary conditions of the positive and contrapositive to answer some of the question stems?
NazAugust 5, 2015
I would recommend re-watching the entire lesson on Sufficient & Necessary statements one more time. You can, however, see this mentioned in the Rules portion of the lesson with the example of "All carrots are vegetables."
C ==> V not V ==> not C
Mehran clearly points out at the end of this slide that it is possible to have a vegetable that is not a carrot. This is the exact idea I pointed out to you in the previous thread.
Hope that helps! Please let us know if you have any other questions.
