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How addition and subtraction are linked
Textbook: Part 2, lesson 64, pp. 50–51
GoalAddition and subtraction as operations and how they are linked.
New words
operation · operatsiya (amal)increase by · orttirishdecrease by · kamaytirishconnection · bog‘liqlik
Explanation
An action that changes an object is called an operation. Adding (+) and subtracting (−) are operations: increase 83 by 100 and we get 183; decrease 378 by 80 and we get 298. If 278 + 395 = 673, then 395 + 278 = 673, 673 − 278 = 395 and 673 − 395 = 278. If one addend grows by 1, the sum grows by 1 too.
Worked examples
If 278 + 395 = 673, then 279 + 394 = 673 (one addend grew by 1, the other fell by 1).
Tashkent has 139 rainy days a year. Dry days: 365 − 139 = 226. Check: 226 + 139 = 365.
Class activity
“Operation machine”: one child plays the “machine” wearing a sign “+100”. Another child says a number and the machine says the result. Then check with the opposite operation.
Practice
1
Knowing 278 + 395 = 673, find 673 − 278.
395
2
Knowing 278 + 395 = 673, find 279 + 396.
675
3
Decrease 378 by 80.
298
4
In January 14 days were cloudy and 6 fewer days were sunny. How many sunny days?
8