Sal's gym holds a hot yoga class with space for 20 people. When the price is $4.50, the class fills up completely. Seeing the desire, Sal raises the price to $5.50. But only 10 people come to the next class. What is the price elasticity of demand for the hot yoga class?
a) 0.20
b) 0.50
c) 3.33
d) 2.50