2
Review: three-digit numbers
Textbook: Part 1, lesson 2, pp. 7–9
GoalReview adding and subtracting three-digit numbers and using properties of sums and differences.
New words
three-digit number · uch xonali sonregrouping · guruhlashsum · yig‘indidifference · ayirma
Explanation
Three-digit numbers are added and subtracted in columns, place by place. To make work easier we use properties: addends can be regrouped, and subtracting a sum can be done step by step: a − (b + c) = a − b − c.
Worked examples
405 + (95 + 27) = (405 + 95) + 27 = 500 + 27 = 527.
850 − (250 + 418) = 850 − 250 − 418 = 600 − 418 = 182.
Class activity
“Sum-and-difference relay”: two teams take turns solving three-digit problems at the board. A team that finds a convenient method earns an extra point.
Practice
1
348 + 275 = ?
623
2
700 − 268 = ?
432
3
Calculate: 840 − (340 + 125).
375
4
A bus travelled 247 km on the first day and 189 km on the second. How many km did it travel in total?
436
5
Compare without calculating: 526 + 184 and 526 + 148. Which sign goes between them (<, >, =)?
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