\(\frac{X}{39.5}=\frac{Y}{(100-39.5)}\)
\(\Rightarrow Y=39.5=X \times(100-39.5)\)
or, \(\quad {\rm{X}} = \frac{{12.5 \times 39.5}}{{60.5}} = 8.16\,\Omega \)
\({\text { When } X \text { and } Y \text { are interchanged } l_{1} \text { and }(100} \)
\({\left.-l_{1}\right) \text { will also interchange so, } l_{2}=60.5\, \mathrm{cm}}\)