Primary Four Third Term Mathematics Lesson Note

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WEEK 1

TOPIC: ESTIMATING LENGTH AND COMPARING MEASUREMENT

SUBTOPIC: ADDITION AND SUBTRACTION OF LENGTH

BEHAVIOURAL OBJECTIVES: At the end of the lesson, pupils should be able to:

1. Estimate distance in kilo meter and meters.
2. Add lengths to kilo meters and meters
3. Solve quantitative aptitude problems on length.

CONTENT

ESTIMATING LENGTH AND COMPARING MEASUREMENT

To estimate means to give an approximate, rather than an exact figure. It means

Making a guess that is accurate or near accurate. Either way, be sure to estimate.

Do not shy away from giving estimates. Practice regularly until you can estimate short lengths in cm with accuracy.

Converting meters to kilometers and vice versa

Nasif lives in the village. He walks to the school which is about half a kilometre from the

village. It takes him about 8 minutes to walk to school.

1 kilometre (km) = 1000 metres (m).

So Nasif walks 500 metres to school.

Long distances are measured in kilometres. Think of distances that are measured in

kilometres. The length of rivers, the distance from one city to another, the rail track, etc.

Examples

Study these examples of converting kilometres to metres.

Example 1:  2 km to metres

=2×100

=2000 meters

Example 2: 4 km 250 m to meters

= (4×1000m)+250m

=4000m+250m

=4250m

Example 3:4.758m

4.758×1000

=4758m

Exercise 2

1. Convert the following to meters.

1.8 km 2.9 km 3.10 km 4.7 km 615 m 5.6 km 400m 6.1 km 625 m 7.2 km 19 m 8.15 km 215 m 9.3 km 100 m 10.8 km 23 m

B .Convert the following to meters.

1.716 km 2.5.782 km 3.2.139 km 4.8.791 km 5.0.920 km 6.7.1 km 7.5.4 km 8.9.7 km 9.0.09 km 10.4.7 km

To change from metres to kilometres you divide by 1000.

Examples

1.Convert 1586 m to kilometre

1586 ÷ 1000

1586 km = 1.586 km =

1 km 586 m

2. Convert 678 m to kilometres

678 ÷ 1000

678.0 km = 0.678 km = 0 km 678 m

Exercise 3

1. Express in kilometres. Remember the position of the decimal point.

1.345 m 2.150 m 3.755 m 4.48 m 5.66 m 6.495 m 7.899 m 8.675 m 9.4 m 10.95 m

1. Convert the following to kilometres and metres.

1.9600 metres 2.8800 metres 3.4525 metres 4.3333 metres 5.1750 metres 6.6112 m 7.7009 m 8.2010 m 9.3165 m10. 1038 m

ADDITION INVOLVING LENGTH

A                                                                        B

C                                                                        D

Line AB is 13 centimetres long while, line CD is 9 centimetres long.

We write AB = 13 cm

CD = 9 cm

The total length of two lines is: 13 cm + 9 cm = 22cm

The difference in their length is: 13 cm −9 cm = 4 cm

We write these as:

AB + CD = 13 cm + 9 cm = 22 cm and AB − CD = 13 cm −9 cm = 4 cm

ADDITION OF LENGTHS IN KILOMETERS AND METERS

7KM+3KM=

645+ 24m=

1. A swimming pool is 120 metres long. Michael swims 6 laps. What distance did he cover in 6 laps?

2. The average weekly distance travelled by a marketer is 320 kilometres. How far does he travel in a year?

3. A limosine car is 800.5 cm long. Calculate its length in metres.

4. An oil pipe is to be made 16.8 m long. It is made into three equal sections.16.8m

a) How long is each section?

b) How long would each section be if it were split into seven equal sections?

5. a)Find one half of a ball of string measuring 21.2 m long.

b)Find one-quarter of the same ball of string.

6. Kalu is walking to his friends house which is 10.5 kilometres away. He walks one-third of the distance and then takes a rest.

a) How far did he walk before taking a rest?

b) How far has he still to walk?

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