7.2×5.8+0.72×42这道题怎么简便计算

7.2×5.8+7.2×4.2
=7.2×(5.8+4.2)
=7.2×10
=72

7.2*(5.8+4.2)

7.2×5.8+0.72×42
=10×0.72×5.8+0.72×10×4.2 //把7.2和42拆成0.72×10和4.2×10
=0.72×10×(5.8+4.2) //提取公因式0.72×10
=7.2×10
=72

0.72*(10*5.8+42)=0.72*100=72

1)7.2×5.8+0.72×42 2)7.2×5.8+0.72×42
=7.2×5.8+7.2×4.2 =0.72×58+0.72×42
=7.2×(5.8+4.2) =0.72×(58+42)
=7.2×10 =0.72×100
=72 =72
题中主要方法如下：两个数相乘，一个数缩小（扩大）若干倍，则另一个数将要扩大（缩小）相同的倍数，结果相等。