SOLUTION: A father and son can build a fence in 30 days. The father can finish the in 40 days. How many days are needed if the son was to put the fence himself?

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A father and son can build a fence in 30 days. The father can finish the in 40 days. How many days are needed if the son was to put the fence himself?      Log On


   

Question 270192: A father and son can build a fence in 30 days. The father can finish the in 40 days. How many days are needed if the son was to put the fence himself?
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
The equation we need for this is
(1/f)(x) + (1/s)(x) = 1
where
f = father time
s = son time
x = time together
-----
we know that x = 30, f = 40. We get
(i) %281%2F40%29%2A30+%2B+%281%2Fs%29%2A30+=+1
step 1 -
multiply by the common denominator of 40s to get
(ii) 30s+%2B+1200+=+40s
step 2- subtract s to get
(iii) 1200+=+10s
step 3 - divide to get
(iv) s+=+120