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

nikkim on April 14, 2020

The relationship between Statistics 9AM and Statistics 3PM

Hey! In the video, I was still confused about this rule: 1) She cannot take world history if she takes statistics at 9AM Naturally, when we diagram this rule, it looks like a "not both" situation. However, it was explained that this is not the case because it is "not binary" and there are "two options" for statistics. I was still confused on that explanation. It seems as if Statistics 9AM and Statistics 3PM could be treated as two different variables? What would be the consequences if we wrote the rule and proceeded with the game using the "not both" situation?

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Skylar on April 15, 2020

@nikkim, happy to help!

"She cannot take World History if she takes Statistics at 9 A.M."
S(9) -> not WH
WH -> not S(9)

We can think of this as a "not both" rule between World History and Statistics at 9 A.M. specifically.

However, we cannot think of it as a "not both" rule between World History and Statistics in general. This is because she could still have both a World History and a Statistics class, it would just have to be the 3 P.M. Statistics class.

If we incorrectly took this rule to mean that she could not have both WH and any S offering, then we would be adding an extra restriction and excluding the valid possibility that WH and S(3) exist together.

We need to keep in mind that there are two different types of Statistics offerings, but they are part of the same overall course.

Does that make sense? Please let us know if you have any other questions!

nikkim on April 17, 2020

Great explanation, thank you!