1.5 Rounding and estimation — Practise with help

1. $20$.
2. $350$.
3. $5$.

Find the digit in the place value you are rounding to, then look at the digit on its right.

(a) $6\,480$. (b) $6\,500$. (c) $6\,000$.

For 1 d.p. look at the hundredths digit; for 2 d.p. look at the thousandths digit.

(a) $5.7$. (b) $5.68$.

Leading zeros are not significant. The first significant figure is the $3$.

The first two significant figures are $3$ and $4$; the next digit is $9 \geq 5$, so round up: $0.003\,5$.

$38 \approx 40$ and $21 \approx 20$.

$40 \times 20 = 800$. (The exact answer is $798$.)

Rounding up the first two digits may carry into the next column.

The first two significant figures are $4$ and $9$; the next digit is $9$, so round up. $49$ becomes $50$, so the answer is $5\,000$.

Round to the nearest pound for the estimate.

Estimate: $£19 + £33 = £52$. Exact: $£51.49$. The estimate is close, so the exact answer is reasonable.

Nearest pound: look at the tenths. 1 s.f.: look at the second digit.

Nearest pound: $£39$. 1 significant figure: $£40$.