Posted by Anonymous on .
if Steven can mix 20 drinks in 5 minutes, Sue can mix 20 drinks in 10 minutes, and Jack can mix 20 drinks in 15 minutes, how much time will it take all 3 of them working together to mix the 20 drinks?

math 
Reiny,
Steve's Rate = 20/5 drinks/minute = 4 dr/min
Sue's rate = 20/10 d/min = 2 dr/min
Jack's rate = 20/15 dr/min = 4/3 dr/min
combined time = 20/(4+2+4/3)
= 2.73 minutes or
2 minutes and 44 seconds.