6.9×9.9+31×0.99的简便方法

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6.9×9.9+31×0.99的简便方法6.9×9.9+31×0.99的简便方法6.9×9.9+31×0.99的简便方法6.9×9.9+31×0.99=6.9x10-6.9x0.1+31x1-31x0

6.9×9.9+31×0.99的简便方法
6.9×9.9+31×0.99的简便方法

6.9×9.9+31×0.99的简便方法
6.9×9.9+31×0.99
=6.9x10-6.9x0.1+31x1-31x0.01
=69-0.69+31-0.31
=69+31-0.69-0.31
=100-1
=99