77
Parts of quantities
Textbook: Part 3, lesson 77, pp. 19–21
GoalWriting small units as shares of a larger unit: length and mass.
New words
decimetre · detsimetrcentimetre · santimetrkilogram · kilogrammgram · gramm
Explanation
Small units of measure are shares of larger units. 1 m = 10 dm, so 1 dm = 1/10 m. 1 m = 100 cm, so 1 cm = 1/100 m. 1 mm = 1/1000 m. In the same way 1 g = 1/1000 kg. Several small units make several shares of the big unit: 37 cm = 37/100 m.
Worked examples
7 cm is 7/100 of 1 m, because 1 m = 100 cm.
1/4 of 1 kg: 1 000 g : 4 = 250 g.
Class activity
“Measuring tape”: children split a 1 m ribbon or rope into 10 equal parts, see that each part is 1/10 m (1 dm), and write pieces of different lengths as fractions.
Practice
1
How many centimetres is 1/10 of 1 m?
10
2
What part of 1 m is 37 cm?
37/100
3
How many grams is 1/4 of 1 kg?
250
4
How many kilograms is 3/10 of 1 t?
300
5
How many centimetres is 1/5 of a 2 m ribbon?
40