F, G, and H are not interchangeable because of the conditions imposed by the question stem.
Let's run through the set-up quickly.
We know that six textbooks will each be evaluated over six weeks. There are three I textbooks - F, G, and H - and three A textbooks - X, Y, and Z.
Each textbook will be evaluated once by J and once by R.
J: _ _ _ _ _ _ R: _ _ _ _ _ _ 1 2 3 4 5 6
Rule 1 - R cannot evaluate any I textbook until J has evaluated that textbook
Therefore, R cannot evaluate any I textbook during Week 1 and J cannot evaluate any I textbook during Week 6.
Rule 2 - J cannot evaluate any A textbook until R has evaluated that textbook.
Therefore, J cannot evaluate any A textbook during Week 1 and R cannot evaluate any A textbook during Week 6.
Rule 3 - R cannot evaluate any two I textbooks consecutively
Rule 4 - J must evaluate X during Week 4
The question stem also tells us that J evaluates H during Week 3 and R evaluates G during Week 6.
What do we know so far?
J: _ _ H X _ _ R: _ _ _ _ _ G 1 2 3 4 5 6
Rule 1 tells us that R cannot evaluate any I textbook until J has evaluated that textbook. Therefore, R must evaluate H after Week 3.
Rule 3 tells us that R cannot evaluate any two I textbooks consecutively. This means that R cannot evaluate H during Week 5. Therefore, R must evaluate H during Week 4 and R must evaluate A textbooks during Weeks 3 and 5.
J: _ _ H X _ _ R: _ _ A H A G 1 2 3 4 5 6
This severely restricts the placement of F. R cannot evaluate F until after J has evaluated it. As there are only two weeks left open on R's schedule and we deduced above that R cannot evaluate any I textbook during Week 1, R must evaluate F during Week 2. This means that J must evaluate F during Week 1.
Hope this helps! Please let us know if you have any further questions.
