Which one of the following could be the list of the four courses Alicia takes?

on December 24, 2019

She cannot take Japanese if she takes Macroeconomics.

I am wonder how you knew that this rule is a "not both" rule and that it should only be put in the "out" pile?

1 Reply

on January 3, 2020

Hello @mamie,

"She cannot take Japanese if she takes Macroeconomics."

This rule basically tells us that Japanese and Macroeconomics cannot coexist. They may both be out, but they cannot both be in. I will demonstrate.

"If she takes Macroeconomics" is our sufficient condition. "Cannot take Japanese" is necessary.

M - - - - - - - - > not J

Now let's look at the contrapositive.
J - - - - - - - - -> not M

We now know that one of the three spaces in our out-group must be reserved for either J or M.