Answer to Question #111224 in Discrete Mathematics for Martin

Question

b) Suppose that b is small and d is large, and further that either b and d are identical or that c is a
tetrahedron. Max believes that c must be a tetrahedron on the basis of this information. Which of
the following is true of this situation?

1. Max is correct to believe that we can determine the shape of c but it is not a tetrahedron,
since the given information is contradictory.
2. Max is mistaken, and nothing can be concluded about c, after all c is only mentioned in
one of the disjuncts of a disjunction.
3. Max is correct, because there is no situation in which b is small, d is large and b and d are
names of the same objects.
4. Max is correct, because it there is no situation in which b is small, d is large, and c is a
cube.

Answer 1

Answer: 3. Max is correct, because there is no situation in which b is small, d is large and b and d are names of the same objects. 

You cannot consider one object to be both large(d) and small(b). So, b and d are not identical. Then, from second condition we can assume that c is tetrahedron. So, Max is correct and his reasoning is correct too.