During Kinetic study of reaction $\mathrm{2 A+B \rightarrow C+D}$, the following results were obtained :

	$\mathrm{A [M]}$	$\mathrm{B [M]}$	initial rate of formation of $\mathrm{D}$
I	0.1	0.1	$6.0\times10^{-3}$
II	0.3	0.2	$7.2\times10^{-2}$
III	0.3	0.4	$2.88\times10^{-1}$
IV	0.4	0.1	$2.40\times10^{-2}$

Based on above data, overall order of the reaction is _________.