During Kinetic study of reaction 2 A + B → C + D, the following results were obtained: Based on above data, overall order of the reaction is ____.

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

	A [M]	B [M]	initial rate of formation of D
I	$\displaystyle 0.1$	$\displaystyle 0.1$	$\displaystyle 6.0 \times 10^{-3}$
II	$\displaystyle 0.3$	$\displaystyle 0.2$	$\displaystyle 7.2 \times 10^{-2}$
III	$\displaystyle 0.3$	$\displaystyle 0.4$	$\displaystyle 2.88 \times 10^{-1}$
IV	$\displaystyle 0.4$	$\displaystyle 0.1$	$\displaystyle 2.40 \times 10^{-2}$

Based on above data, overall order of the reaction is $\displaystyle \_\_\_\_$.