<PRE><B>Question 112784</B>
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?
:
The completed job is the mixing of 20 drinks. 
Let the completed job = 1
:
Let t = time required when working together:
:
{{{t/5}}} + {{{t/10}}} + {{{t/15}}} = 1
:
Multiply the equation by 30 to get rid of those annoying denominators:
30*{{{t/5}}} + 30*{{{t/10}}} + 30*{{{t/15}}} = 30(1)
:
Cancel them denominators and you have:
6t + 3t + 2t = 30
11t = 30
t = {{{30/11}}}
t = 2.73 minutes for all three to mix 20 drinks
:
Convert the decimal portion to seconds: .73 * 60 = 43.6 seconds
2 min 43.6 sec</PRE>