Answer:
7 percent
Step-by-step explanation:
We have the following information from the question:
The probability that a student chooses art as an elective is 15 percent: 
The probability that a student chooses art or drama is 20 percent: 
The probability that a student chooses both art and drama is 2 percent:

Recall that:

We plug in the various probabilities to get:




Hence the probability that a student chooses drama as an elective is 7 percent