加法运算律练习1.28+97=97+2855+27+45=27+(55+45)136-25-75=136-(25+75)a+b=b+aa+b+c=b+(a+c)a-b-c=a-(b+c)2.306+58=300+6+60-2=360+4=364 37+84+63+16=(37+63)+(84+16)=100+100=200538-129-71=538-(129+71)=538-200=338 754-(54+79)=754-54-79=700-79=6213.a+b 150 160 170 180 190 200 210a |