a) The diagram shows that 16% of the students plays only the piano, 13% of the students plays only the violin, and 5% of the students plays both instruments.
So, the percentage of students playing the piano is 21%, because you can choose a students who plays only the piano (16%) or a student who plays both instruments (5%)
b) We can't answer this question without knowing the number of students in the school. In fact, we only know that 5% of the students plays both instrument. This means that, if the total number of students is , the number of students who play both instruments is
And it is impossible to evaluate this quantity without knowing the value for x.
c) Since the probability of N is 21% (see point a), the probability of not N will be
d) By the same logic, the probability of V is percent. So, we have
e) We have
And we just computed the probability of to be 0.34. So, we have