109
Quantities and their properties
Textbook Part 3, pp. 72–73
GoalUse the commutative property when adding quantities; restate “bigger–smaller” the other way round.
New words
commutative law · o‘rin almashtirish qonunipastry chef · qandolatchimixture · qorishma
Explanation
The commutative law works for quantities too: 25 cm + 74 cm = 74 cm + 25 cm = 99 cm. If a teapot is bigger than a cup, then the cup is smaller than the teapot. Both sentences say the same thing.
Worked examples
A pastry chef mixed 2 kg sugar, 4 kg flour and 2 kg butter: 2 + 4 + 2 = 8 kg of mixture.
21 dm + 78 dm = 78 dm + 21 dm = 99 dm
Class activity
“Flip it” game: the teacher says “The wardrobe is wider than the stove.” Children flip it: “The stove is narrower than the wardrobe.”
Practice
1
25 cm + 74 cm = ?
99 cm
2
Finish: “If the rolling pin is longer than the knife, the knife is ...”
shorter than the rolling pin
3
“If the flour is lighter than the sugar, the sugar is ...”
heavier than the flour
4
2 kg + 4 kg + 2 kg = ?
8 kg