80÷2+100÷5=                                        45-20×3÷4=

　　240÷6-2×15=                                         52-36÷3+20=

　　320-200÷5×8=                                       140-20×5+25=

　　20×30+20×40=                                      25×(30+10)=

　　800÷40-400÷40=                                   (840-400)÷4=