\(u =(100 \pm 0.2)-(80 \pm 0.2)=(20 \pm 0.4)\,cm\)

\(v =(180 \pm 0.2)-(100 \pm 0.2)=(80 \pm 0.4)\,cm\)

From lens formula,

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f} \Rightarrow \frac{1}{f}=\frac{1}{80}-\frac{1}{-20}\)

\(f=16\,cm\)

Also \(\frac{\Delta v}{v^2}+\frac{\Delta u}{u^2}=\frac{\Delta f}{f^2}\)

\(\Rightarrow \frac{\Delta f}{f} \times 100=\left(\frac{\Delta v}{v^2}+\frac{\Delta u}{u^2}\right) \times f \times 100\)

\(\Rightarrow \% f=\left(\frac{0.4}{400}+\frac{0.4}{6400}\right) \times 16 \times 100\)

\(=1.70\)