94
Multiplication can be done in any order
Textbook: Part 3, lesson 88, pp. 36–37
GoalThe order property: swapping the factors does not change the product.
New words
swapping places · o‘rin almashtirishproperty · xossaconvenient method · qulay usulrow · qator
Explanation
When the factors swap places the product stays the same: a × b = b × a. For example 3 rows of 5 jars and 5 rows of 3 jars are both 15 jars. This makes counting easier: instead of adding 3 ten times we can use 10 × 3 = 30.
Worked examples
7 × 2 = 2 × 7 = 14.
3 × 100 = 100 × 3 = 100 + 100 + 100 = 300.
Class activity
“The tray”: children arrange 2 rows of 7 paper buns, then turn the tray and say what changed (the rows) and what did not (the total).
Practice
1
Amir counted 3 rows of 5 jars (5 × 3), Aziz counted 5 rows of 3 jars (3 × 5). Who counted more?
Equal: both counted 15
2
6 × 10 = 10 × 6 = ?
60
3
A carton holds 2 l of juice. A customer bought 12 cartons. How many litres?
24
4
One bag holds 3 kg of flour. How many kg are in 20 bags?
60
5
One notebook costs 3 thousand so‘m. How many thousand so‘m do 100 notebooks cost?
300