All of the cargo ships of the Blue Star Line are over 100 meters long, and all of its passenger ships are under 100 m...
FatimaMay 20, 2020
under 100m is necessary condition
Hi!
So this is probably a dumb question, but I have to ask and make sense of it. (I also apologize for my English, not a native)
So I understand the video explanation that we are looking for a ship that is under 100m, because SS coral at the dock. However, when we write out the diagram from passage, under 100 m is the necessary condition, like
GS - -> after 1980 and <100m
when we are looking for the answer, I thought we couldn't go against the arrow direction to get the answer Gold star line. could you help me with that thought process?
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Thanks for the question! So you’re right that being under 100m is a necessary condition. Let me pull out the important parts of the stimulus for this question. There’s a couple of variables we need to keep track of here. There’s two companies, Blue Star Line and Gold Star line. There’s also two types of ships, passenger ships and cargo ships. The first sentence tells us:
Blue star line cargo ship —> Over 100m
Then, we’re told later that
Gold star line passenger/cargo —> Built after 1980, under 100m
Then we’re told
Port Tropica —> Less than 100m
OK. So now we’re told that the SS. Coral is a cargo ship that’s docked at Port Tropica. Well, we know two things now. One: it’s a cargo ship, not a passenger ship. Two: it has to be less than 100m, since it’s docked at Port Tropica. But then this tells us something else. Let’s take a look at the contrapositive of the first sentence:
~Over 100m —> ~Blue star line cargo ship
And here, we have to keep in mind that over 100m and under 100m are going to be negatives of each other here. If it’s under 100m, it’s not over 100m. But that means it’s not a blue star line cargo ship. And from this, we further know that it’s not a blue star line ship, because it’s a cargo ship, not a passenger ship. This means it’s a gold star line cargo ship (since only blue star and gold star can dock their boats are Port Tropica), and we know that all gold star line passenger and cargo ships are built after 1980. So we know that this ship was built after 1980.
Hope this helps! Feel free to ask any other questions that you might have.
FatimaMay 21, 2020
And here, we have to keep in mind that over 100m and under 100m are going to be negatives of each other here. If it’s under 100m, it’s not over 100m. - After reading this I got it! Thank you Shunhe!
