12.5×5.78+3×78
=12.5×（5+0.7+0.08）+3×78
=12.5×5+12.5×0.7+12.5×0.08+3×78
=62.5+12.5×0.7+12.5×0.08+3×78
=62.5+8.75+1+234
=71.25+1+234
=72.25+234
=306.25
这道题主要用了乘法分配律的逆运算，和125的乘法，全程可以口算。请参考！
12.5×（5+0.78）+3×78
=12.5×5+12.5×0.78+3×78
=62.5+0.125×78+3×78
=62.5+78×（0.125+3）
=62.5+78×3.125
=62.5+（80-2）×3.125
=62.5+80×3.125-2×3.125
=62.5+250-6.25
=306.25
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