Maria normally spends a half-hour driving to work. When her average speed is ten miles per hour slower than usual, the trip takes ten minutes longer. How many miles does she drive to work?

Answer 1

s*(1/2) = (s-10)(1/2 + 1/6)
s = 40

check:
40mi/hr * 1/2 hr = 20 mi
30mi/hr * 2/3 hr = 20 mi