# If Alicia takes Statistics at 3 P.M. and Geography, then which one of the following courses must she also take?

on October 22, 2019

Stumped

I was able to narrow my answers down to J R and M but since the rules says J/R and J/M I couldn't tell which one had to be in. It would seems that either of them could be in. For example you could have J and R in together or you could have R and M in together. J appeared twice in the options so I chose J as my answer. Could you explain why R is the correct answer? Thanks!

Replies

Irina on October 22, 2019

@tomgbean

If A takes S at 3 pm and G, which of the following courses must she take?

She needs to choose four courses out of 7 - G J M P R S (9 am and 3 pm) and WH. We know that she takes S at 3 pm and G.

S G __ __

We can infer that she cannot take P because this would require her to take statistics at 9 am.
We can infer that she cannot take WH because she must take either G or WH but not both.
Thus the only remaining classes she could choose from are J M R. The rules tell us that she cannot take J if she takes M, meaning she can only take either J or M:

M -> ~ J
J -> ~ M

Since we have three courses to choose from and we can only pick 1 out of M/J, we know that she must definitely take R and either M or J, so the full course listing could be either:

(1) S G R J
(2) S G R M

Let me know if this makes sense and if you have any further questions.

on October 22, 2019

Got it!Thanks!

on June 21, 2021

I also narrowed it down to J R M but then got confused. Couldn't we have also said that she had to take (J or R) (either or ) and therefore must take M?