Question 746637
John can paint the fence around his house in 15 hours, while his brother chad can do it in 18 hours.
 If John paints for 7 hours alone and turns the rest over to chad, how long will it take chad to finish painting the fence?
:
Let t = time for Chad to finish the fence
Let the completed job = 1; (a painted fence)
:
A typical shared work equation
{{{7/15}}} + {{{t/18}}} = 1
multiply eq by the least common multiple of 15 & 18; that's 90, results:
6(7) + 5t = 90
5t = 90 - 42
t = 48/5
t = 9.6 hrs for Chad to finish the job
:
:
Check this on a calc`: 7/15  +  9.6/18  = 1