Do Now:

47°

6.2m

x

θ

16cm

13cm

5.8m

54.3°

Rounding DecimalsHow many decimal places do each of these

numbers have?• 4.1• 70• 6.45• 0.9873• 0.007• 456.88

Rounding DecimalsWhen rounding decimals:• keep the required number of decimal places• if the next digit is < 5 (less than 5) keep the final

required digit the same and drop all the unwanted digits off

• if the next digit is ≥ 5 (greater than or equal to 5) round up by adding 1 to the final required digit and then dropping off all the unwanted digits.

ExamplesRound the following decimals to the number of decimalplaces indicated in the brackets

a) 25.679 (1 dp)

b) 0.0450 (3 dp)

c) 56.2798 (2 dp)

d) 1.04998 (3 dp)

When solving a problem the answer should always be rounded to a sensible number of decimal places. The number of decimal places a number is rounded to should be written in brackets after the answer.

A 150cm plank of wood is divided into seven pieces. How long is each piece?

21.428 571cm

It would be sensible to round this answer to 1dpor 2dp.

Recap of rounding decimals1) Round 4.875 to 2dp2) Round 0.027942 to 2dp3) Round 11.0498 to 3dp4) A family uses 3578 litres of water in one week.

How much water does the family use, on average, per day? (Round your answer to the nearest litre)

5) Here are the rainfall amounts for the five months of May, June, July, August and September.

59.3cm, 18.28cm, 25.91cm, 79.307cm and 18.4cmWhat is the total rainfall for this five-month period?

4.88

0.03

11.050

511L

201.2cm

Significant Figures

• How many significant figures do these numbers have:

200 103001500 993.5 1015.08 5 000 0000.0073 0.04011

Zeros are significant when they are: inbetween other numbers Both at the end of a number and after the first non-zero digit after the

decimal place.Examples: 9.703 (4sf) 27.40 (4sf)

Zeros are not significant when they are: At the front of a number At the end of a number with no decimal pointExamples: 0.036 (2sf) 24 000 (2sf)

When rounding, using significant figures, it is often necessary to use zeros as place holders.

Examples• Round 389 to 1 significant figure

• Round 2136 to 1 significant figure

• Round 47 to 1 significant figure

• Round 6451 to 2 significant figures

More examples....• Round 0.04275 to 2 significant figures

• Round 0.0035 to 1 significant figure

• Round 0.060784 to 3 significant figures

Some for you to try:3556 (1sf)

4368 (2sf)

417.3 (1sf)

0.00975 (2sf)

1843 (2sf)

654.9589 (4sf)

4400

400

0.0098

1800

655.0

4000

10Ticks worksheetL6 P3 pg 19