60
Review: calculations with three-digit numbers
Textbook: Part 2, pp. 36–37
GoalUnit review: three-digit numbers, addition, subtraction, expressions.
New words
review · takrorlashexpression · ifodaconvenient way · qulay usulperimeter · perimetr
Explanation
In this lesson we review reading and comparing three-digit numbers, addition and subtraction, expressions with brackets, convenient calculation and perimeter. Brackets are done first. In a row of additions and subtractions we go from left to right: 80 − 17 − 13 = 63 − 13 = 50.
Worked examples
(62 + 37) − 32: first 99, then 99 − 32 = 67.
A rectangle 10 cm by 6 cm: perimeter 10 + 6 + 10 + 6 = 32 cm.
Class activity
“Review relay”: two teams. The board has three kinds of tasks (comparing, expression, problem). Each child solves one and passes to the next player.
Practice
1
(62 + 37) − 32 = ?
67
2
80 − 17 − 13 = ?
50
3
Compare: 4 hundreds 3 tens 5 ones and 3 hundreds 9 tens 7 ones.
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4
900 seats were set aside for a party and 745 people came. How many seats stayed empty?
155