12
Adding up to a round number (31 + 9)
Textbook: Part 1, lesson 12, pp. 26–27
GoalPractise adding up to a round number; grouping addends in a convenient way.
New words
convenient way · qulay usulgrouping · guruhlashminute · daqiqa (minut)talk / presentation · ma’ruza
Explanation
We solve 72 + 8 by splitting: 72 + 8 = 70 + (2 + 8) = 70 + 10 = 80. When adding many numbers it is easy to add first those that make a whole ten: 4 + 7 + 6 + 3 = (4 + 6) + (7 + 3) = 20.
Worked examples
29 + 1 = 30; 76 + 4 = 80; 25 + 5 = 30.
64 cm + 6 cm = 70 cm; 21 dm + 9 dm = 30 dm.
Class activity
“Find your pair”: each child gets a card from 1 to 9. Children find the partner whose number makes 10 together and hold hands.
Practice
1
46 + 4 = ?
50
2
64 sm + 6 sm = ? sm
70
3
12 + 8 + 15 + 5 = ?
40
4
Three pupils spoke for 4, 7 and 5 minutes. How many minutes in all?
16