107
Writing masses as decimals
Textbook: Part 3, lesson 107, pp. 112–113
GoalWriting mass as a decimal: the link between t, kg and g.
New words
mass · massatonne · tonnakilogram · kilogrammgram · gramm
Explanation
1 t = 1 000 kg, so 1 kg = 0.001 t. 1 kg = 1 000 g, so 1 g = 0.001 kg. Therefore 512 g = 0.512 kg; 700 kg = 0.7 t; 2 kg 384 g = 2.384 kg; 6 t 125 kg = 6.125 t. To add and subtract masses, change the decimals into common fractions: 5.3 t + 1.9 t = 5 3/10 + 1 9/10 = 6 12/10 = 7 2/10 = 7.2 t.
Worked examples
461 g = 0.461 kg; 30 kg = 0.03 t.
9 kg − 3.6 kg = 8 10/10 − 3 6/10 = 5 4/10 = 5.4 kg.
Class activity
“With the scales”: children weigh flour or rice on kitchen scales (with an adult's permission) and write the result in grams and in kilograms (for example 350 g = 0.35 kg).
Practice
1
Write 461 g in kilograms as a decimal.
0.461
2
Write 4 kg 718 g in kilograms as a decimal.
4.718
3
Write 836 kg in tonnes as a decimal.
0.836
4
Work out 5.3 t + 1.9 t (in t).
7.2
5
Work out 9 kg − 3.6 kg (in kg).
5.4