Hi @katia, thanks for your post. Great question. Let's take a look.
The local rule on this question is that R is the second song performed. The last rule provided in the game setup establishes that the song played after R is played on the keyboard (k), and that song is right before N. So here, R is the second song; whatever the third song is will be played on the keyboard (k); and N is the fourth song played.
This leaves two songs: Q, and S. One has to be played first, and one has to be played third.
We also know from the original game rules that the first song cannot be played on the flute (f). If R is the second song performed, then the third song will be played on the keyboard (k). This leaves two instruments: the guitar (g) and the harmonica (h).
Answer choice (D) says N is played on the guitar (g). If N, the fourth song, is played on the guitar (g), then the first song will have to be played on the harmonica (h).
If the first song is played on the harmonica (h), then that song is not R (which we know in this question is played second).
The contrapositive of the second rule tells us that if R is not played on the harmonica (h), then S cannot be played on the keyboard (k). This would mean that the third song cannot be S.
Also, if N, the fourth song, is played on the guitar (g), then the contrapostiive of the third rule comes into play: if N is not played on the flute (f), then Q cannot be played on the keyboard (k). This would mean that the third song cannot be Q.
We are out of options. If neither Q nor S can be played on the keyboard (k) third, that slot will stay blank, which violates the parameters of this game (four songs are played consecutively means NO blanks allowed). So (D) must be eliminated, it cannot be true.
Hope this helps! Please let us know if you have any additional questions.
