Jeff and Kirk can build a

Question

Jeff and Kirk can build a 75-ft retaining wall together in 8 hours. because jeff has more experience, he could build the wall by himself 1 hour quicker than Kirk. How long would it take Kirk ( to the nearest minute) to build the wall by himself?

Answer 1

1/J + 1/K = 1/8

J=k-1

1/(K-1) + 1/k = 1/8

multiply by 8K(K-1) to get

8K + 8K-8 = K(K-1)

K^2 -17K +8 =0

K= 17/2 + (1/2)sqr225

K= 17/2 + 15/2 = 32/2 = 16 hours = 16x60 = 960 minutes

Notice that if J and K worked at the same speed, they'd both do it alone in 16 hours (8x2)

but one if slightly faster than the other so it turns out they do it in 16 and 15 hours each.