Question

I don't get how to do this.

Answer 1

Answer:

426 chickens

Step-by-step explanation:

let the pigs = x

the ducks = 2×x = 2x

the chickens = 3×(2x) = 6x

x +2x +6x = 639

9x=639

x = 639/9 = 71

the chickens = 6x = 6×71 = 426

Answer 2

Answer:

$426\:\mathrm{chickens}$

Step-by-step explanation:

Since a duck has two legs, a pig has four legs, and a chicken has two legs, we can write the following system of equations:

$\begin{cases}d+p+c=639,\\d=2p,\\c=3d\end{cases}$, where $d$ is the number of ducks on the farm, $c$ is the number of chickens, and $p$ is the number of pigs.

Substituting, we get:

$d+\frac{1}{2}d+3d=639,\\4.5d=639,\\d=\boxed{142}$

Now substitute $d=142$ into $c=3d$ to get the number of chickens:

$c=3(142)=\boxed{426\:\mathrm{chickens}}$