1.09×2.5=27.25 .(判断对错)
0.8+0.8+0.8+0.8+0.8= .
301×312=312×300+1. .
先乘前两个数,或者先乘后两个数,积不变,这是乘法结合律. .
0.0023×2100=0.23×21=23×0.21 .
0.25×43+0.75×19= .