Charles is a stay-at-home parent who lives in Philadelphia and provides math tutoring for extra cash. At a wage of $50 per hour, he is willing to tutor 10 hours per week. At $65 per hour, he is willing to tutor 19 hours per week.
Using the midpoint method, the elasticity of Charles's labor supply between the wages of $50 and $65 per hour is approximately , which means that Beth's supply of labor over this wage range is .