Условие:

Вычисли удобным способом.
7 + 8 + 3 + 2
6 + 2 + 8 + 4
18 + 11 + 2 + 9
17 + 5 + 5 + 3

7 + 8 + 3 + 2 = (7 + 3) + (8 + 2) = 10 + 10 = 20
6 + 2 + 8 + 4 = (2 + 8) + (6 + 4) = 10 + 10 = 20
18 + 11 + 2 + 9 = (18 + 2) + (11 + 9) = 20 + 20 = 40
17 + 5 + 5 + 3 = (17 + 3) + (5 + 5) = 20 + 10 = 30