(1)码旦1.2×2.5+0.8×2.5=(1.2+0.8)×2.5=2×2.5=5(举枝2)迟答扰8.16÷0.25÷40=8.16÷(0.25×40)=8.16÷10=0.816(3)2.5×7.9×0.8=(2.5×0.8)×7.9=2×7.9=15.8