SOLUTION: Mr. jenkins can dig a ditch in one hour less time than his son. working together they can do the job in 2/3 hrs. how long does it take mr. jenkins to do the job alone?

Question 501029: Mr. jenkins can dig a ditch in one hour less time than his son. working together they can do the job in 2/3 hrs. how long does it take mr. jenkins to do the job alone?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
Mr. jenkins can dig a ditch in one hour less time than his son.
working together they can do the job in 2/3 hrs.
how long does it take mr. jenkins to do the job alone?
:
Let t = time for Mr. J to do the job alone
Let the completed job = 1; (a dug ditch)
:
Let's do this in minutes
2/3 hr = 40 min
and
(t+60) = time required by the son alone
;
A typical shared work equation
+ = 1
:
Multiply by t(t+60); results
40(t+60) + 40t = t(t+60)
:
40t + 2400 + 40t = t^2 + 60t
80t + 2400 = t^2 + 60t
Arrange as a quadratic equation
t^2 + 60t - 80t - 2400 = 0
t^2 - 20t - 2400 = 0
factors to
(t-60)(t+40) = 0
positive solution
t = 60 min or 1 hr for Mr. J to do the job
:
:
you can check this in the original equation
+ =
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