A metre scale is balanced on a knife edge at its centre. When two coins, each of mass $10 \mathrm{g}$ are put one on the top of the other at the $10.0 \mathrm{cm}$ mark the scale is found to be balanced at $40.0 \mathrm{cm}$ mark. The mass of the metre scale is found to be $x\times {10}^{-2} \mathrm{kg}$. The value of $x$ is _____ .