Posted by Jay on .
Stephanie can clean a pool in 1 hour , and Mark can clean the same pool in 1.5 hours. If the rate at which they work together is the sum of their rates working separately, how many minutes should they need to clean the pool if they work together? (1 hr=60 min)

Math 
Marth,
Stephanie cleans at the rate of 1 pools/hr.
Mark cleans at the rate of 1/1.5, or 2/3 pools/hr.
Their combined rate is 5/3 pools/hr
If r is the rate, t is time, and p is the number of pools, then
r = p/t
(5/3pools/hr) = (1 pool)/t
t = 3/5hr
t = 60*3/5 = 36min