Scan options before you calculate. If values differ by orders of magnitude, estimate powers of ten and units first.
Use divisibility and last-digit checks for integers. For percentages, benchmark against simple fractions like one-half or one-third.
Reserve exact methods for tight clusters where two options sit close together—precision matters there.
Rounding rules
When options differ by orders of magnitude, round aggressively after checking the first significant digit direction.
Sanity checks
Ask whether the answer order matches the story—population counts should not look like percentages.