Don't get why D is incorrect

@mbarnett, Let's look at the setup for this game. We need to match grades ABCDE to courses Ec, G, H, I, P, R. Since we have 6 courses and only 5 grades to choose from, we will end up with at least one identical grade. __ __ __ __ __ A B C D E Let's look at the rules: (1) G & P are consecutive meaning it could be A &B, B&C, C&E etc. we can diagram this rule as: GP v. PG (2) I &R are consecutive but we have no information on the exact order so it could be: IR v RI (3) Ec grade is higher than H E>H __ __ __ __ __ A B C D E ~H ~E (4) G grade is higher than P G>P combined with rule (1) we can determine that P must immediately follow G: GP __ __ __ __ __ A B C D E ~H ~E ~P ~G Now, the question gives us additional rules to determine the order: P grade is higher than Ec and Ec grade is higher than any language P > Ec > I > R Combined with the rules above, we can determine the following: GP > Ec > H > IR > RI Let's diagram this: /R /H /I /R G P Ec /H /I __ __ __ __ __ A B C D E ~H ~E ~P ~G We can determine the grades for G, P, and Ec but for the rest of the subjects we only know that H is lower than Ec, but we have no rule whether H & Ec are consecutive, so H could be D or E. We also know that Ec is higher than either I or R are that I &R are consecutive but we do not know whether I or R grade is higher, so either Ec -C, R -D, I-E or Ec-C, I-D, R-E could be the correct order. What information do we need to determine all of the grades? Let's look at (D) - R & H are identical. This fact alone would still result in two possible combinations of courses & grades. Option 1: H G P Ec R I __ __ __ __ __ A B C D E Option 2: H G P Ec I R __ __ __ __ __ A B C D E Since H &R could either be E or D, we cannot determine the complete order of the grades. The correct answer choice (E) tells us that H is higher than R. This fact allows us to conclude that H & I are D and R is E. H G P Ec I R __ __ __ __ __ A B C D E Does this make sense? Let me know if you have any other questions.

Quick q: doesn't "E" always come directly before "H". And "H" always come after "E" according to the rules. Because rule 3 and 4 are identical. In rule 4 "P" always comes after "G".

Hi, we know that P and G are consecutive from the first rule, not the fourth. The third rules does not tell us that E and H are consecutive, so they do not have to be.