A galvanometer has a full scale deflection current of 10 mA and it has a small internal resistance of $20 \mathrm{\Omega }\text{.}$ The resistance to be connected in series with it to convert it into a voltmeter of range 0 to 10 V is ${\mathrm{R}}_1$. The resistance to be connected in series with it to convert it into a voltmeter of range 0 to 20 V is ${\mathrm{R}}_2$ . The ratio ${\mathrm{R}}_1 / {\mathrm{R}}_2$ is nearly equal to