$$ \begin{aligned} & \begin{array}{l} \chi=1.2 \times 10^{-5} \\ \quad \mu_r=1+\chi=1+1.2 \times 10^{-5} \end{array} \end{aligned} $$ Fractional Change $$ \begin{aligned} & =\frac{\Delta \mathrm{B}}{\mathrm{~B}}=\frac{\mu_0 \mu_{\mathrm{r}} \mathrm{ni}-\mu_0 \mathrm{ni}}{\mu_0 \mathrm{ni}}=\left(\mu_{\mathrm{r}}-1\right) \\ & =1.2 \times 10^{-5} \end{aligned} $$