Which one of the following is an acceptable selection of fish and plants for the aquarium?

jaberges December 29, 2020

Unless Condition- Game Set Up

Hi, I was confused about the game setup for this set of questions. I thought that "unless" introduces necessary conditions and that I should negate the sufficient condition. When I watched the game set up explanation, you had not negated the sufficient condition. I am confused if there are certain circumstances when one would negate the sufficient and circumstances where one wouldn't. Thank you for your help. EX: "she cannnot select the H unless she selects the K" I wrote this as "not H---> K" the explanation wrote this as "H-->K"

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shunhe January 5, 2021

Hi @jaberges,

Thanks for the question! So you weren’t wrong— “unless” can be thought of as introducing the necessary condition, and then negating the sufficient condition. So X unless Y is diagrammed

~X —> Y

Or the contrapositive is just

~Y —> X

So as long as you take one element and put it in the sufficient and negate it, you’re good.

Now here, the sentence we have is “she cannot select the H unless she selects the K.” So remember, unless introduces the necessary, and then we have to negate the sufficient, so this is ??~(Cannot select the H) —> K

And “not cannot” cancels out, since it’s a double negative. Remember, what you’re negating is already a “not” statement, so the resulting statement has to be positive. So this ends up simplifying to

H —> K

which is what the explanation wrote.

Hope this helps! Feel free to ask any other questions that you might have.

PhoebeIman May 7, 2021

I had the same question and this was helpful. Thank you!