87900089800 9999991000000 58万580000 420×2842×280
999999×2=1999998
999999×3=2999997
999999×4=3999996
76×20= 514﹣300= 3.4+6= 9÷9%= 24×=
÷= 62= 8.7+= ﹣0.8= ﹣×0=