In the mythical nation of Oz, gasoline used to sell for $1 a gallon, and the natives purchased 100,000 gallons a week. Four years ago, the price rose to $3 a gallon, and the natives reduced their quantity demanded to 90,000 gallons a week. Calculate the price elasticity for this change. Today, gas again sells for $1 a gallon in Oz, but the natives are only buying 70,000 gallons a week. What gives?