The rectangular block shown in the figure below is subjected to tension within the elastic range. The increase in the length of $a$ is $a$:$=2\mathrm{.}70*{10}^{-3}in.$ and the contraction of $b$ is $b$:$=-3\mathrm{.}50*{10}^{-4}in.$ If the original lengths of a and $b$ were $ai$:$=2in$ and $bi$:$=1in,$ respectively, what is Poisson's ratio for the material of the specimen?