1. METRIC LINEAR UNITS(CENTIMETER AND DECIMETER)
GRADE 3

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Hello, How are you doing?
Today, we are going to start a new lesson on Linear units.

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Unit
Unit is defined as a fixed amount that is used as a standard of measurement.
Example –
Length of the pencil is 4 cm - standard unit
Length of the pencil is 4 paper clips – nonstandard unit

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Length
The measurement of distance between two end points.
Example – The length of the pen is 6 centimeter.

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Metric system
Metric System – A group of units based on measuring by tens.
Various units of metric systems.
Kilometer
Decimeter
Centimeter
Meter

6. Model to find the length of the object
Line up to the left end of the object to the 0 mark on the ruler.
Find the closer centimeter mark to the right end of the object.
Record the length.

7. Find the length of the line segment
The length of the line segment is 6 cm.

8. Centimeter and decimeter
Centimeter (cm) and decimeter (dm) are the units of measuring lengths.
1 decimeter (dm) = 10 centimeter (cm)

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Tips to Remember
Decimeter (dm) is bigger unit than centimeter (cm)
For measuring small objects, centimeter (cm) is used.
Example – eraser, pencil
For measuring bigger objects, decimeter (dm) is used.
Example – book, length of magazine

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Conversion of units
Decimeter can be changed to centimeter by multiplying with 10.
Example –
4 dm = 4 x 10 cm
= 40 cm

11. The actual length of the pencil is 1dm. What is the length in cm?
Answer- 1 x 10 = 10 cm

12. Which is smaller in length?
12 dm
150 cm
190 cm
13 cm

13. About how much distance can be covered in 1 minutes?
15 cm
15 dm
30 cm
30 dm

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Convert 164 cm to dm.
Answer – 16.4 dm

15. Estimate the length of wrist watch.
15 cm
15 dm
5 cm
5 dm

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ASSESSMENT

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1. Which is about 5 cm long?
Pencil
Book
Door
wall

18. 2. Which is true about the ray shown in the scale?
5 cm long
5/10 dm long
½ dm long
All the above

19. 3. Choose the best estimate.
Your thumb is about --- long.
5 cm
5 dm
5 m

20. 4. Estimate the length of your finger nail.
1 cm
2 dm
1 dm
10 cm

21. 5. Which unit will you use to find the length of the door?cm dm
Either a or b
None of the above

22. 6. Which unit can be best used to describe the length of your arm?cm dm
None of the above

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7. Fill in the Blanks.
12 dm = --- cm
89 dm = --- cm
Answer –
120
890

24. Express the following in cm. a) 11 dm b) 55 dm

25. 9. Compare using <, > or =
a) 32 dm  320 cm
b) 70 dm  70 cm
Answer- =
>

26. 10. Which tool can be best used to find the length of the book?
Meter scale
Centimeter scale
Measuring tape

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Recap
Unit
Length
Metric system
Model to find length of the object
Centimeter and Decimeter
Conversion of units
Solved Examples
Practice Problems

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Well Done!
Now Practice worksheets on the lesson.