2.5X(1.2+0.8)=5
1.2×2.5+0.8×2.5=(1.2+0.8)×2.5=2×2.5=5
1.2乘2.5加0.8乘2.5=(1.2+0.8)×2.5=2×2.5=5
1.2x2.5+0.8x2.5=(1.2+0.8)x2.5=2x2.5=5