Consider the following single step reaction in gas phase at constant temperature. $$ 2 \mathrm{~A}_{(\mathrm{p})}+\mathrm{B}_{(\mathrm{g})} \rightarrow \mathrm{C}_{(\mathrm{p})} $$ The initial rate of the reaction is recorded as $r_1$ when the reaction starts with 1.5 atm pressure of A and 0.7 atm pressure of B . After some time, the rate $r_2$ is recorded when the pressure of $C$ becomes 0.5 atm . The ratio $r_1: r_2$ is $\_\_\_\_$ $\times 10^{-1}$. (Nearest integer)