2.5×3/7+0.4÷2又1/3=2.5×3/7+0.4×3/7=(2.5+0.4)×3/7=2.9×3/7=87/70=1又17/70
2.5x3/7+0.4÷2又1/3=2.5×3/7+0.4÷7/3=2.5×3/7+0.4×3/7=(2.5+0.4)×3/7=2.9×3/7=29/10×3/7=87/70