Question 160195
If Steven can mix 20 drinks in 5 min, Sue can mix 20 drinks in 10 min, and 
Jack can mix 20 drinks in 15 min. How much time will it take all 3 of them
 working together to mix the 20 drinks? 
:
Let t = time required when they all work together
:
Let the completed job = 1 (the mixing of 20 drinks)
:
Each will do a fraction of the job, which added together, will = 1
:
{{{t/5}}} + {{{t/10}}} + {{{t/15}}} = 1
:
Clear the denominators, multiply equation by 30, results:
6t + 3t + 2t = 30
:
11t = 30
t = {{{30/11}}}
t = 2.727 min or about 2 min 43.6 sec. all working together
:
:
Check solution on calc:
{{{2.7/5}}} + {{{2.7/10}}} + {{{2.7/15}}} =
.54 + .27 + .18 = .99 ~ 1