## Elementary Technical Mathematics

$$2.5 \ km^2.$$
Since $1\ ha =10^4 \ m^2 =\frac{10^4}{10^6}\ km^2$, so $1\ ha = 10^{-2} \ km^2$. Now, to change $ha$ to $km^2$, we multiply by $10^{-2}$. That is, $$250 \ ha=250\times 10^{-2} \ km^2=2.5 \ km^2.$$