\(\frac{X}{Y}\,\, = \,\frac{{20}}{{100 - 20}}\,\, = \,\,\frac{1}{4}\,\,\,\,\,\,.......\,\,(1)\)
હવે \(\,\frac{{4X}}{Y}\,\,\, = \,\,\,\frac{\ell }{{(100 - \ell )}}\)
\( \Rightarrow \,\,\,\,4\,\, \times \,\,\frac{1}{4}\,\,\, = \,\,\,\frac{\ell }{{(100 - \ell )}}\,\,\,\) \(\therefore \,\,\,\ell \,\, = \,\,\,50\,\,cm\)