Of the final grades received by the students in a certain math course, 1/5 are A's, 1/4 are B's, 1/2 are C's, and the remaining 10 grades are D's. What is the number of students in the course??
Assume that the total number of students in the course is 'x'.
According to the given conditions, the total number of students who received:
- A's = x(1/5) = x/5
- B's = x(1/4) = x/4
- C's = x(1/2) = x/2
- D's = 10
Therefore, x/5 + x/4 + x/2 + 10 = x
<=> x - (19/20)x = 10
<=> x/20 = 10
<=> x = 200
The answer is D.