1. Ms. Roberts' class had a test in which 1/8 of the students got A's. On the next test, 3/8 of the students got A's. How many of the students received A's on one of the two tests?

This is a great problem about overlaping sets. It has many possible answers. It is not possible to find a unique right answer because we don't know how many students got A's on both tests (though in my experience, it is likely that most if not all of the students who got A's on the first test also got A's on the second). The answer would be 1/2, if none of the students who got A's on the first test got A's on the second, and it would be 3/8 if all of the students who got A's on the first test also got A's on the second. Or it could be some fraction in between. A great critical thinking problem, but if you want to write a problem where the answer is 1/8 + 3/8, you need to change the problem like this:

1. Ms. Roberts' class had a test in which 1/8 of the students got A's. On the next test, a different 3/8 of the students got A's. How many of the students received A's on one of the two tests?