Question 834235
Jeff and kirk can build a 75 ft retaining wall together in 7 hours
 because Jeff has more experience he can build it alone in two hours quicker than kirk.
 how long can it take kirk to build the wall alone? round to the nearest minute.
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Let t = time required by Jeff to build the wall
then
(t+2) = time required by Kirk
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Let the completed job = 1 (a completed wall)
:
Each will do a fraction of the wall, the two fractions add up to 1
{{{7/t}}} + {{{7/((t+2))}}} = 1
multiply by t(t+2), to clear the denominators, resulting in:
7(t+2) + 7t = t(t+2)
7t + 14 + 7t = t^2 + 2t
14t + 14 = t^2 + 2t
A quadratic equation
0 = t^2 + 2t - 14t - 14
t^2 - 12t - 14 = 0 
Using the quadratic formula, the reasonable approx answer
t = 13.071 hrs
Kirk takes 2 hrs longer, therefore
15.071 hrs for Kirk
Find the hrs and minutes
15 + ..071(60) = 15 hrs 4 minutes
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