-2.8+2.8,-- , ÷ , -0.990
x
6
3
y
2
a
1-+= 1÷×= 7-= 65÷0.05=
7÷×7×= 2÷2%= 0÷0.1-0.1×1= (+)×24=
2.5,-4,- , 4