SOLUTION: Jeff and kirk can build a 75 ft retaining wall together in 7 hours because Jeff has more experience he can build alone in two hours quicker than kirk. how long can it take kirk to

Question 834235: Jeff and kirk can build a 75 ft retaining wall together in 7 hours because Jeff has more experience he can build alone in two hours quicker than kirk. how long can it take kirk to build the wall alone? round to the nearest minute.
thank you I am so stuck on this question I don't know what to do
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
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.
:
Let t = time required by Jeff to build the wall
then
(t+2) = time required by Kirk
:
Let the completed job = 1 (a completed wall)
:
Each will do a fraction of the wall, the two fractions add up to 1
+ = 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
:
:
Did this make sense to you?

RELATED QUESTIONS
Jeff and Kirk can build a 75 ft retaining wall together in 8 hours. Because Jeff has more (answered by josgarithmetic)

Jeff and Kirk can build a 75-ft retaining wall together in 7 hours. Because Jeff has... (answered by ikleyn)

Jeff and Kirk can build a 75ft wall together in 10 Hours. Because Jeff has more... (answered by josgarithmetic)

Jeff & Kirk can build a 75- ft retaining wall together in 9 hours. Because Jeff has more... (answered by fractalier)

Jeff and Kirk can build a 75-ft retaining wall together in 5 hours. Because Jeff has... (answered by ikleyn)

Jeff and Kirk can build a 75-ft retaining wall together in 4 hours. Because Jeff has... (answered by ankor@dixie-net.com)

Jeff and Kirk can build a 75 ft wall together in 3 hours. Jeff has more experience, he... (answered by josgarithmetic)

a mason can build a wall in 6 hours less than an apprentive. together they can build the... (answered by ptaylor)

a mason can build a wall in six hours less than an apprentice. together they can build... (answered by josgarithmetic)