After polling a class of 20 music students by a show of hands, you find that 8 students play the guitar and 9 students play the piano. Given that information, what is the minimum number of students in this music class who play both the guitar and the piano?
The correct answer is A.
To find the minimum number of students in a class of 20 who play both guitar and piano when 8 play guitar and 9 play piano, you must look at the range for which the guitar and piano players may overlap. For instance, all 8 who play guitar could also play piano; that's the maximum.
The minimum would be the smallest overlap they can have. In this case, there are 20 total; the two groups could be disjoint because 9 + 8 or 17 is less than 20. Thus, the minimum is 0.