1.2×3/4=1.2×3÷4=1.2÷4×3=0.3×3=0.9；
2/5×1.25=1.25×2÷5=2.5÷5=0.5；
所以1.2×3/4-2/5×1.25=0.9-0.5=0.4
1.2x(3/4)-(2/5)x1.25
=(6/5)x(3/4)-(2/5)x(5/4)
=(1/4)(1/5)(6x3-2x5)
=(1/20)x8
=8/20
=2/5
1.2×3/4-2/5×1.25
=0.3x3-0.4x1.25
=0.9-0.5
=0.4
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