SOLUTION: A farmer can plow a field in 12 hours by using one tractor. His son, using a different tractor can plow it in 10.5 hours. How long will it take the farmer and his son working toget

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A farmer can plow a field in 12 hours by using one tractor. His son, using a different tractor can plow it in 10.5 hours. How long will it take the farmer and his son working toget      Log On


   

Question 411522: A farmer can plow a field in 12 hours by using one tractor. His son, using a different tractor can plow it in 10.5 hours. How long will it take the farmer and his son working together to plow the field?
Found 2 solutions by rfadrogane, richwmiller:
Answer by rfadrogane(214) About Me  (Show Source):
You can put this solution on YOUR website!
A farmer can plow a field in 12 hours by using one tractor. His son, using a different tractor can plow it in 10.5 hours. How long will it take the farmer and his son working together to plow the field?
Sol'n:
rate x time = 1
1/12+1/10.5 = 1/x
1/x = 5/28
x = 28/5
x = 5.6 days ----answer
^_^

Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
1/a+1/b=1/x
1/12+1/10.5=1/x
10.5/126.0+12/126.0=1/x
22.5/126.0=1/x
x=126.0/22.5
x=5.6 hours working together
check
x/a+x/b=1
x/12+x/10.5=1
5.6/12+5.6/10.5=1
0.46666667+0.53333333=1
1.0=1
ok