Question

一点2×8点9-7点九的简便运算怎样简便。

一点2×8点9-7点九的简便运算怎样简便。

Answer 1

一点2×8点9-7点九
=1.2x8.9-7.9
=1.2x（9-0.1）-7.9
=1.2x9-1.2x0.1-7.9
=10.8-0.12-7.9
=2.78

Answer 2

1.2×8.9-7.9
=1.2×8.9-8.9+1
=(1.2-1)×8.9+1
=0.2×8.9+1
=1.78+1
=2.78