1) (2/5+a)+3/5; 3) (a+2/3)+1/3;2) (2,4+b)+1,6; 4) (b+1,5)+0,5;5) (a+1

1) (2/5 + а) + 3/5 = а + (2/5 + 3/5) = а + 1
2) (2,4 + b) + 1,6 = b + (2,4 + 1,6) = b + 4
3) (a + 2/3) + 1/3 = a + (2/3 + 1/3) = a + 1
4) (b + 1,5) + 0,5 = b + (1,5 + 0,5) = b + 2
5) (a + 1 1/4) + 3/4 = a + (1 1/4 + 3/4) = a + 2
6) (b + 2,9) + 1,1 = b + (2,9 + 1,1) = b + 4