2
Review: operations with multi-digit numbers
Textbook: Part 1, lesson 2, pp. 7–9
GoalColumn addition and subtraction of multi-digit numbers; using properties of addition to calculate conveniently.
New words
column · ustuncommutative property · o‘rin almashtirish xossasiassociative property · guruhlash xossasiconvenient way · qulay usul
Explanation
In column form we write the digits place under place and work from right to left. In addition we may swap and regroup the addends: a + b = b + a, (a + b) + c = a + (b + c). Grouping addends that make a round number makes the work easy. Check a subtraction like this: difference + subtrahend = minuend.
Worked examples
37 + 289 + 63 = (37 + 63) + 289 = 100 + 289 = 389.
1 000 − 345 − 455 = 1 000 − (345 + 455) = 1 000 − 800 = 200.
Class activity
“Round pairs”: cards show numbers such as 37, 63, 375, 625, 120, 880. Children find pairs whose sum is 100 or 1 000.
Practice
1
Calculate conveniently: 203 + 456 + 197.
856
2
Work out 12 345 + 8 679 in column form.
21024
3
Work out 50 000 − 17 384.
32616
4
A shop took 24 750 sum on Monday, 31 680 sum on Tuesday and 18 570 sum on Wednesday. How many sum did it take in the three days?
75000