All bridges built from 1950 to 1960 are in serious need of rehabilitation. Some bridges constructed in this period, ...
finleykeJune 2, 2016
I'm lost
For some reason I can't track this one at all.. I suppose I am having problems figuring out what is diagram able .. I get the somes and the sufficient and necessary conditions there.. I guess I am failing to make the deduction .. Although I know technically I should be able to..I have no idea why this one is tripping me up.. But it is..
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Hey @finleyke, thanks for your question. No problem. Let's break it down and be sure that you're getting each component correct, ok?
All bridges built from 1950 to 1960 are in serious need of rehabilitation.
50/60 - > SNR
Some bridges constructed in this period, however, were built according to faulty engineering design.
50/60-some-FED
At least some bridges in serious need of rehabilitation are not suspension bridges.
SNR-some-not SB
No suspension bridges are among the bridges that were built according to faulty engineering design.
SB - > not FED
All right. We can combine the first and second sentences, as follows:
FED-some-50/60 [remember, "some" statements are reversible] - > SNR
Therefore:
FED-some-SNR
That is answer choice (C): Some bridges that were built according to faulty engineering design are in serious need of rehabilitation.
Hope this helps! And good luck tomorrow!
LucasJuly 27, 2019
The part of the diagramming I am most confused about is the "no SS bridges" part at the end of the stimulus. When it's a NO statement, according to sufficient and necessary rules, you can pick X or Y as variables. I left it alone and diagrammed it the way it was in the stimulus, but in the video the guy did it the opposite way. Would I still get the right answer?
RaviJuly 27, 2019
@noname,
Great question. You would still get the right answer, as you would be diagramming the contrapositive of what was diagrammed in the video.
Suspension bridge - >not faulty design
Faulty design - >not Suspension bridge
The important thing to remember is that with "no" statements, you're negating the necessary condition. Pick either variable, put it in the necessary condition, and negate it. The other variable is the sufficient condition. Both statements mean the same thing, they're just the contrapositive for each other.
Does that make sense? Let us know if you have any other questions!
