SAT Mathematics Practice Test 2

The amount of money the performer earns is directly proportional to the number of people who attend the performance. Thus, by the definition of direct proportionality, M=kP, where M is the amount of money the performer earns, in dollars, P is the number of people who attend the performance, and k is a constant. Since the performer earns 120 when 8 people attend the performance, one can substitute 120 for M and 8 for P, giving 120=8k. Hence, k=15,and the relationship between the number of people who attend the performance and the amount of money, in dollars, the performer earns is M=15P. Therefore, when 20 people attend the performance, the performer earns 15(20)=300 dollars.Choices A, B, and D are incorrect and may result from either misconceptions about proportional relationships or computational errors.