Question

1.2乘以8.9再减去7.9的简便方法怎么做

Answer 1

1.2×8.9-7.9
=1.2×（1+7.9）-7.9
=1.2+1.2×7.9-7.9
=1.2+7.9×（1.2-1）
=1.2+7.9×0.2
=1.2+1.58
=2.78