Teach me to sanity-check [a
calculation] with a rough
estimate first. The method,
then three examples where the
estimate catches a plausible
arithmetic mistake.

Estimate Before Calculating

The rough answer that catches the wrong precise one.

Prompt

Teach me to sanity-check [a type of calculation] with a rough estimate first. Give me the estimation method, then three worked examples where the estimate would have caught a plausible arithmetic mistake.