Which of the following arguments (i.e., logical calculations) reach logically valid conclusions, and which do not? Which argument utilizes the logical rule of modus ponens?

If Fred got an A in the course, then he must have done all the work. Fred did get an A in the course, so therefore he didn’t do all the work.

If Fred got an A in the course, then he must have done all the work. Fred did get an A in the course, so therefore he must have done all the work.

If Fred got an A in the course, then he must have done all the work. Fred did do all the work in the course, so therefore he did get an A.

If Fred got an A in the course, then he must not have done all the work. Fred didn’t get an A in the course, so therefore he must not have done all the work.