With no calculators allowed in the PMDC MDCAT, physics questions are engineered to test proportional scaling, orders of magnitude, and unit analysis rather than tedious arithmetic.
When a question asks "If the radius of a wire is halved, what happens to its resistance?", do not plug in $3.14159$ for $\pi$. Use proportionality:
$$R = \rho \frac{L}{A} = \rho \frac{L}{\pi r^2} \implies R \propto \frac{1}{r^2}$$
If $r \to r/2$, then $R \to \frac{1}{(1/2)^2} = 4R$. The resistance quadruples instantly.