Explanation:
\({A = 3.0k\,\Omega ,\Delta A = 0.1k\,\Omega }\)
\({B = 9.0k\,\Omega ,\Delta B = 0.3k\,\Omega }\)
Now, equivalent parallel resistance \(R_{P}\) is given by,
\({\frac{1}{{{R_p}}} = \frac{1}{{\;A}} + \frac{1}{{\;B}}{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} (1)}\)
\({\therefore \quad {R_p} = \frac{{AB}}{{A + B}} = \frac{{3 \times 9}}{{3 + 9}}}\)
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {R_p} = 2.25\,k\,\Omega }\)
Differentiating equation (1), we get,
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \frac{{ - \Delta {R_P}}}{{R_p^2}} = \frac{{ - \Delta A}}{{{A^2}}} - \frac{{\Delta B}}{{{B^2}}}}\)
\({\therefore \quad \Delta {R_P} = \Delta A{{\left( {\frac{{{R_P}}}{{\;A}}} \right)}^2} + \Delta B{{\left( {\frac{{{R_P}}}{B}} \right)}^2}}\)
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} = (0.1){{\left( {\frac{{2.25}}{{3.0}}} \right)}^2} + (0.3){{\left( {\frac{{2.25}}{{9.0}}} \right)}^2}}\)
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} = 0.05625 + 0.01875}\)
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \Delta {R_P} = 0.075\,\,k\Omega }\)
\(\therefore\) Percentage error in equivalent resistance is,
\({\frac{{\Delta {R_P}}}{{{R_P}}} \times 100 = \frac{{0.075}}{{2.25}} \times 100}\)
\({{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} = 3.33\% }\)