\(\frac{{{R_1}}}{{{R_2}}} = {\left( {\frac{{{l_1}}}{{{l_2}}}} \right)^2} = {\left( {\frac{{100}}{{200}}} \right)^2}\) \( \Rightarrow \) \({R_2} = 4{R_1}\)
\(\frac{{\Delta R}}{R} \times 100 = \frac{{{R_2} - {R_1}}}{{{R_1}}} \times 100 = \frac{{4{R_1} - {R_1}}}{{{R_1}}} \times 100\)\( = 300\% .\)