求几道简便运算题 五年级寒假作业的！！急急急

2.5×1.25×32 =2.5×1.25×4×8 =2.54×8×1.25 =10×10 =100 （10＋0.1＋0.01）×39 =10×39+0.1×39+0.01×39 =390+3.9+0.39 =394.29 6.19×2.05＋79.5×0.619 =6.19×2.05＋7.95×6.19 =6.19×(2.05+7.95) =61.9 0.86＋9.9×8.6 =8.6×0.1+9.9×8.6 =8.6×(0.1+9.9) =86