4.2×7.8+2.5×4.2
=4.2x（7.8+2.5）
=4.2x（10+0.3）
=4.2x10+4.2x0.3
=42+1.26
=43.26
希望能帮到你！
简便计算
4.2×7.8+2.5×4.2
=4.2×（7.8+2.5）
=4.2×10.3
=4.2×10+4.2×0.3
=42+1.26
=43.26
如图
4.2×7.8+2.5×4.2
=4.2×7.8+2.2×4.2+0.3*4.2
=4.2*（7.8+2.2）+1.26
=4.2*10+1.26
=43.26
4.2×7.8+2.5×4.2
=4.2x(7.8+2.5)
=4.2x(10+0.3)
=4.2x10+4.2x0.3
=42+0.72
=42.72
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