Вычислите, применяя переместительное и сочетательное свойства сложения : 1) 1 2/7 + 2 5/6 + 3 5/7+ 1 1/6; 3) 2 1/5 + 3/8 + 1 4/5 + 5/8 ; 2) 4/9 + 1 2/3 + 2 5/9 + 1/3 ; 4) 1 3/10 + 1/4 + 2 7/10 + 3/4 . с объяснением.

1) 1 2/7 + 2 5/6 + 3 5/7 + 1 1/6 = (1 2/7 + 3 5/7) + (2 5/6 + 1 1/6) = (4 7/7) + (3 6/6) = 5 + 4 = 9 2) 2 1/5 + 3/8 + 1 4/5 + 5/8 = (2 1/5 + 1 4/5) + (3/8 + 5/8) = (3 5/5) + (8/8) = 4 + 1 = 5 3) 4/9 + 1 2/3 + 2 5/9 + 1/3 = (4/9 + 2 5/9) + (1 2/3 + 1/3) = (2 9/9) + (1 3/3) = 3 + 2 = 5 4) 1 3/10 + 1/4 + 2 7/10 + 3/4 = (1 3/10 + 2 7/10) + (1/4 + 3/4) = (3 10/10) + (4/4) = 4 + 1 = 5