Chapter Summary

Approximation vs estimation

• Approximation = rounding a given number.
• Estimation = guessing an unknown quantity.

The 5 significant figure rules

1. All non-zero digits are significant.
2. All zeros between non-zero digits are significant.
3. Leading zeros in decimals are not significant.
4. Trailing zeros after the decimal point are significant.
5. Trailing zeros in whole numbers are ambiguous (context-dependent).

Key practices

• Answers: 3 significant figures when the value is not exact; 1 decimal place for an angle in degrees; 2 decimal places for money in dollars and cents.
• Working: carry two more than the answer needs, so 5 s.f., or 3 d.p. for an angle, or 4 d.p. for money. Round once, at the end.
• For estimation, round until you can do the sum in your head, and write the rounded values down.