Estimation

#### Tier: #Foundation #Higher

Description

Estimation means finding an approximate answer quickly by rounding values to convenient numbers — usually to 1 significant figure.

$$\frac{48.3 \times 19.7}{4.1} \approx \frac{50 \times 20}{4} = \frac{1000}{4} = 250$$

Method:

1. Round each value to 1 significant figure
2. Carry out the simplified calculation
3. State that the answer is an estimate

Estimation is useful for:

• Checking whether a calculator answer is reasonable
• Answering exam questions that say "estimate" or "use appropriate approximations"

Significant figures reminder: the first significant figure is the first non-zero digit. $0.0034$ rounded to 1 s.f. is $0.003$.

Common error: rounding to 1 decimal place rather than 1 significant figure, giving unnecessarily complex "estimates". Also: not showing the rounded values in working — the method marks require this.

Links

Rounding