In the experimental set up of metre bridge shown in the figure, the null point is obtained at a distance of 40 cm from A. If a 10 Ω resistor is…

In the experimental set up of metre bridge shown in the figure, the null point is obtained at a distance of $\displaystyle 40$ cm from A . If a $\displaystyle 10 \Omega$ resistor is connected in series with $\displaystyle \mathrm{R}_1$, the null point shifts by $\displaystyle 10$ cm. The resistance that should be connected in parallel with $\displaystyle \left(\mathrm{R}_1+10\right) \Omega$ such that the null point shifts back to its initial position is :