[tex]\begin{gathered} Area\text{ of circle = }\pi r^2 \\ 100=3.14r^2 \\ r^2=\frac{100}{3.14} \\ r^2=31.85 \\ r=\sqrt[]{31.85} \\ r=5.64\text{ mm} \end{gathered}[/tex][tex]\begin{gathered} \text{The circumference of a circle = 2}\pi r \\ =\text{ 2 x 3.14 x 5.64} \\ =35.42\text{ mm }\cong35.4\text{ mm (1 decimal place)} \end{gathered}[/tex]
