Cattle eating grass problem _ cattle eating grass problem

"Problem description"

Grass is growing at a uniform pace every day, this piece of grass can be 27 cows for 6 days, or 23 cows for 9 days, so that 21 cows to eat for several days. Solving

Solution: Grassland of the original grass fixed, set to X, grass growth rate per day set to Y, each cow to eat the amount of grass per day set to Z. Set for 21 cows to eat T-day.

The equations are available by:

The 1th and 2 equations (elimination) can be obtained by:

y = 15z, substituting the third equation:

Substituting y = 15z into the first equation (elimination)

x = 72z

So the solution was T =12.

So 21 cows can be eaten for 12 days.