文档介绍：-=               +=       -=              +=              -=   -=             +=               -=     1-=                   +=               5×400= +=               187÷1000=                 1+=
 ×10=                75÷10=                    ÷= ×7=                ×7=                 ×8= ×8=                ×2=                5×= ×=              ×=               ×0=
10×=              ×7=                ×100= ×4=                ×4=                4×= ×8=                ×4=                 ×0= ×50=                30×=                ×3= ×2=                ×=              ×= 1-=               ×=