#18 - Each year, an official estimate of the stock of cod in
Could someone please help me understand why C is incorrect. thanks so much.
Answer Choice C is incorrect because there is no information given in the stimulus by which to draw that inference. The stimulus does not give any information on the accuracy of the two different methods. Since this is a must be true question we are looking for an inference that can be drawn from the information given in the stimulus.
Since the estimate is taken by averaging the two different measurements, and one has gone up over the last ten years by roughly the same amount that the other measurement went up, we know that the most recent estimate should be fairly close to the one that was taken ten years ago because the change in the two measurements will average each other out.
Hope this helps.
I can't really seem to agree your explanations of why A is correct, because to me, "the two estimates usually agreed closely" means what ever numbers they each were, they were the same/similar. For example, that can be research vessels = 9, commercial = 10. OR, research vessels = 5, commercial = 4. It's all RELATIVE. So "agreeing closely" every year doesn't necessarily mean the ABSOLUTE official estimate would be the same, if compared year to year.
Thus, now and 10 years ago might have a completely different ABSOLUTE value of official estimate.
Does anyone understand what I'm trying to say?
The key to understanding this question is the last clause of the final sentence in the stimulus. If the two estimates are moving in opposite directions but at the same rate, and are thus directly inversely proportional, then the average of the two (meaning adding both together and dividing the sum total by 2) would have to be roughly the same. As an example:
Sample A 10 years ago = 100 cod
Sample B 10 years ago = 100 cod
Average 10 years ago = 100 cod
Sample A this year = 200 cod (2x 10 years ago)
Sample B this year = 50 cod (1/2 10 years ago)
Average this year = 100 cod (same as 10 years ago)
Hope this clears things up!