Question

7.8×4.2+78×0.42简便计算

Answer 1

7.8×4.2+78×0.42
=7.8×4.2+7.8×4.2
=7.8×4.2×2
=7.8×8.4
=8.4×（8-0.2）
=8.4×8-8.4×0.2
=67.2-1.68
=65.52

Answer 2

7.8×4.2+78×0.42
可以提取公因数以后进行计算，方法如下
7.8×4.2+78×0.42
=7.8×4.2×10÷10+78×0.42
=(7.8×10)×(4.2÷10)+78×0.42
=78×0.42+78×0.42
=2×78×0.42
=65.52