Question 458867
It takes Rob 10 hours to clean an attic.
 Sam can clean the same attic in 11 hours. 
How long would it take them if they work together?
:
Let t = time if they work together
Let the completed job = 1 (a clean attic)
:
A typical shared work equation 
:
{{{t/10}}} + {{{t/11}}} = 1
multiply by a common denominator, 110
110*{{{t/10}}} + 110*{{{t/11}}} = 110(1)
Cancel the denominators
11t + 10t = 110
:
21t = 110
 t = {{{110/21}}}
 t = 5.238 hrs or about 5 hrs 14.3 min