A metal string A is suspended from a rigid support and its free end is attached to a block of mass M . Second block having mass 2 M is suspended at the bottom of the first block using a string B . The area of cross sections of strings $A$ and $B$ are same. The ratio of lengths of strings of $A$ to $B$ is 2 and the ratio of their Young's moduli $\left(Y_A / Y_B\right)$ is 0.5 . The ratio of elongations in $A$ to $B$ is $\_\_\_\_$ .