Carrie and Crystal live at a equal distances from school. Carries walks to school at an average rate of 3 miles per hour and Crystal rides her bike at an avergae rate of 9 miles per hour. It takes Carrie 20 minutes longer than Crystal to get to school. How far do Crystal and Carrie live?
distanceCrystal=9mi/hr*(time-1/3) 20 min is 1/3 of an hr...
set them equal
t= 1/2 hr
now you can figure the distance from the first equation.posted by bobpursley