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Metre, decimetre, centimetre
Textbook: Part 2, lesson 61, pp. 44–45
GoalThe millimetre – a very small unit of length: 1 cm = 10 mm, 1 dm = 100 mm.
New words
millimetre (mm) · millimetr (mm)ruler · chizg‘ichinsect · hasharotline segment · kesma
Explanation
We measure very small things, like insects, in millimetres. 1 mm is the smallest mark on a ruler. 1 cm = 10 mm, and 1 dm = 10 cm = 100 mm. 6 dm 5 cm 2 mm = 600 mm + 50 mm + 2 mm = 652 mm. To compare, change all lengths into millimetres.
Worked examples
3 dm 4 cm 1 mm = 300 + 40 + 1 = 341 mm.
7 dm 6 mm = 706 mm, 7 dm 6 cm = 760 mm, so 7 dm 6 mm < 7 dm 6 cm.
Class activity
“Tiny measurers”: children measure an eraser, a button, a leaf and a picture of an ant with a ruler and write the result as “… cm … mm” and “… mm”.
Practice
1
3 dm 4 cm 1 mm = ? mm
341
2
7 dm 5 cm = ? mm
750
3
Compare: 7 dm 6 mm and 7 dm 6 cm.
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4
The Red Book lists 21 butterfly species, 6 fly species and 1 dragonfly species. If 54 insect species are listed in total, how many more species are there?
26