For the reaction $\mathrm{A}\to \mathrm{B}+\mathrm{C}$ the following data were obtained: 

$\begin{array}{lccr}t\left(\mathrm{s}\right)& 0& 900& 1800\\ \left[\mathrm{A}\right]& 50.8& 19.7& 7.62\end{array}$

What is the order of the reaction?