naina

• Sep 26th, 2005

 

40 cows graze a pasture  in 40 days,30 cows graze the same pasture in 60 days.
10 cows less graze 20 days more

so 20 cows graze in 60+20 days more which is 80 days

Sivakumar Paramasivam

 Profile Answers by Sivakumar Paramasivam 

• Dec 13th, 2005

 

Ans: 120 days.

Let 'x' be the amount of grazed by a cow per day,

Let 'y' be the growth rate of grass per day,

Let 'z' be the amount of grass present initially,

So, 40 cows can graze (40*x) amount of grass per day and (40*x*40) amount of grass for 40 days.

For 40 days, the growth of grass is (40*y)

So, (40*x*40) = (z + 40*y)

For 30 cows it takes 60 days, so,

(30*x*60) = (z + 60*y)

so, 1600x - 40y - z = 0 ----- 1

     1800x - 60y - z = 0 ----- 2

Subtracting we get, 10x = y , Sub. 10x=y in 1 or 2, we get z = 120y or z = 1200x

For, 20 cows,

20*x*N = z + N*y

Sub, 10x=y and (z=120y or 1200x), we get N = 120

Therefore, for 20 cows it takes 120 days to graze.

Hassan

• Sep 20th, 2006

 

120 Days is correct

nikhil

• Aug 25th, 2014

 

120 Days is correct answer....