21
Adding and subtracting multi-digit numbers (practice)
Textbook: Part 1, lesson 21, pp. 64–66
GoalUse properties of addition and subtraction to calculate conveniently with multi-digit numbers.
New words
convenient method · qulay usulswapping places · o‘rin almashtirishregrouping · guruhlashdate · sana
Explanation
All properties of addition and subtraction work for multi-digit numbers too. Swap addends so that those that make a round sum are next to each other. If you subtract one addend from a sum, the other addend is left. We find the years between dates by subtracting.
Worked examples
58 000 + 836 + 42 000 + 164 = (58 000 + 42 000) + (836 + 164) = 100 000 + 1 000 = 101 000.
(46 280 000 + 9 735 400) − 6 280 000 = 46 280 000 − 6 280 000 + 9 735 400 = 40 000 000 + 9 735 400 = 49 735 400.
Class activity
“Round pairs”: in a row of 8 numbers children find pairs that add up to 100, 1 000 or 10 000 and circle them with the same coloured pencil.
Practice
1
Calculate conveniently: 58 000 + 836 + 42 000 + 164.
101000
2
Calculate conveniently: (46 280 000 + 9 735 400) − 6 280 000.
49735400
3
Calculate conveniently: 825 600 − 125 600 − 290 000.
410000
4
Alisher Navoi was born in 1441 and died in 1501. How many years did he live?
60
5
Calculate conveniently: 5 275 + 640 + 360 + 725.
7000