How many terms will the student need to learn?

Question

There are 25 terms to learn from the exam. 15 of these terms will be on the test, to which the student must define 10. What is the least amount of terms the student will have to learn to guarantee they will know 10 terms on the exam.

Answer 1

Learn just 15 and the 10 not learned may show up, and you only get 5 right

Learn 20 and 5 may show up that were not learned, but you get a guaranteed 10 right

as if you miss 5 of 15, you get the other 10 right

Learn 20 for a guaranteed 10 right, which is 2/3 right or a 67% grade rounded off to an integer percent, a D usually, or maybe D+ but still passing. IF 60% is passing, and 59 % an F, then learn 19 to get a guaranteed 9 right. 9/15 = 3/5 = 60% or D-