SOLUTION: using 2 tractors a farmer can plough a piece of land in 10 days .The farmer uses 2 tractors for the first 4 days and then hires a third tractor.How many days does it take to plough

Algebra ->  Rate-of-work-word-problems -> SOLUTION: using 2 tractors a farmer can plough a piece of land in 10 days .The farmer uses 2 tractors for the first 4 days and then hires a third tractor.How many days does it take to plough      Log On


   

Question 1094216: using 2 tractors a farmer can plough a piece of land in 10 days .The farmer uses 2 tractors for the first 4 days and then hires a third tractor.How many days does it take to plough the piece of land.
Answer by josgarithmetic(39629) About Me  (Show Source):
You can put this solution on YOUR website!
r, work rate for 1 tractor
x, number of days using 3 tractors ("one more tractor")

system%282r%2A10=1%2C2r%2A4%2B3r%2Ax=1%29

r=1%2F20
-
%288%2B3x%29%281%2F20%29=1
3x%2B8=20
3x=12
x=4


4 days with 2 tractors and then 4 days with 3 tractors;
total of 8 days.