freaky

• Nov 30th, 2006

 

I believe it is 20cows for 96 days.

Jaichandran.R

• Feb 13th, 2007

 

Answer is 10.When the days increases from 24 to 60, no. of cows decreases from 70 to 30,hence the reduction in cows for 36 days increment is obtained by half of the previous days cows ,that is 70/2= 35 and 35-5which is equal to 30 , now for the increment of 60 to 96 days can be obtain by half the previous no. of cows ,substract by 5, that is 30/2 which is 15 and 15-5 ,where we get 10.

gaurav4067

 Profile Answers by gaurav4067 

• Dec 5th, 2010

 

g - grass at the beginning
r - rate at which grass grows, per day
y - rate at which one cow eats grass, per day
n - no of cows to eat the grass in 96 days

From given data,
g + 24*r = 70 * 24 * y ---------- A
g + 60*r = 30 * 60 * y ---------- B
g + 96*r = n * 96 * y ---------- C

Solving for (B-A),
(60 * r) - (24 * r)
= (30 * 60 * y) - (70 * 24 * y) 36 * r
= 120 * y ---------- D

Solving for (C-B),
(96 * r) - (60 * r)
= (n * 96 * y) - (30 * 60 * y) 36 * r
= (n * 96 - 30 * 60) * y 120 * y
= (n * 96 - 30 * 60) * y

[From D] 120 = (n * 96 - 1800)
n = 20

Hence, 20 cows are needed to eat the grass in 96 days.