Q.15. A resistance R = 5 $\Omega$ is connected to one of the gaps in a metre bridge, which uses a wire of length I m. An unknown resistance X is in the other gap as shown in the figure. The balance point is noticed at 'l' cm from the positive end of the battery. On interchanging R and X, it was found that the balance point further shifts by 20 cm away from end A. Neglecting the end calculate the value of unknown resistance X used.