under 100m is necessary condition

Hi @Fatima, 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.

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!

Glad I could help!