<PRE><B>Question 695863</B>
10 cows or 25 goats can graze a field in 20 days.
From this we can say a field can be grazed in:
200 cow-days
or
500 goat days
:
How long would 12 cows and 15 goats take to graze the same field?
let d = no. of days with the above animals
let the the grazed field = 1
:
{{{(12d)/200}}} + {{{(15d)/500}}} = 1
Multiply by 1000 to clear the denominators, results:
5(12d) + 2(15d) = 1000
60d + 30d = 1000
90d = 1000
d = 1000/90
d = 11.1 days</PRE>