<PRE><B>Question 489529</B>
It takes my father 3 hours to plow our cornfield with his new tractor.
 Using the old tractor it takes me 5 hours.
 If we both plow for 1 hour before I go to school, how long will it take Dad to finish the plowing?
:
let t = time it takes Dad to finish plowing
let the completed job = 1 (a plowed field)
:
{{{1/5}}} + {{{(t+1)/3}}} = 1
Multiply by 15 to clear the denominators results:
3 + 5(5+1) = 15
3 + 5t + 5 = 15
5t = 15 - 8
5t = 7
t = {{{7/5}}}
t = 1.4 hrs for Dad to finish
:
:
Check solution (Dad plowed for a total of 2.4 hrs)
1/5 + 2.4/3 = 
.2 + .8 = 1; confirms our solution</PRE>