сторінка 30 гдз 2 клас математика Скворцова Онопрієнко 2019

Розв'язання:

Сторінка 30
Використовуємо переставний закон додавання

✔ 1.
2 + 6 = 8
3 + 6 = (2 + 1) + 6 = (2 + 6) + 1 = 8 + 1 = 9
6 + 4 = (6 + 2) + 2 = 8 + 2 = 10
7 + 1 = 8

✔ 2.
2 + 9 = 9 + 2 = (9 + 1) + 1 = 10 + 1 = 11
5 + 7 = 7 + 5 = (7 + 3) + 2 = 10 + 2 = 12
4 + 8 = 8 + 4 = (8 + 2) + 2 = 10 + 2 = 12
3 + 9 = 9 + 3 = (9 + 1) + 2 = 10 + 2 = 12
5 + 6 = 6 + 5 = (6 + 4) + 1 = 10 + 1 = 11
3 + 8 = 8 + 3 = (8 + 2) + 1 = 10 + 1 = 11
6 + 7 = 7 + 6 = (7 + 3) + 3 = 10 + 3 = 13

✔ 3.
6 + 5 = (6 + 4) + 1 = 10 + 1 = 11
14 – 7 = (14 – 4) – 3 = 10 – 3 = 7
15 – 8 = (15 – 5) – 3 = 10 – 3 = 7
5 + 9 = 9 + 5 = (9 + 1) + 4 = 10 + 4 = 14
6 + 8 = 8 + 6 = (8 + 2) + 4 = 10 + 4 = 14
12 – 6 = (12 – 2) – 4 = 10 – 4 = 6
17 – 9 = 17 – (7 + 2) = 17 – 7 – 2 = 10 – 2 = 8
7 + 5 = 7 + (3 + 2) = (7 + 3) + 2 = 10 + 2 = 12
5 + 8 = 8 + 5 = (8 + 2) + 3 = 10 + 3 = 13
13 – 8 = 13 – (3 + 5) = 13 – 3 – 5 = 5

✔ 4.