99.9 ×9.9(巧算) (12.5+2.5)×0.8(巧算)急死人.

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99.9 ×9.9(巧算) (12.5+2.5)×0.8(巧算)急死人.
99.9 ×9.9(巧算) (12.5+2.5)×0.8(巧算)
急死人.

99.9 ×9.9(巧算) (12.5+2.5)×0.8(巧算)急死人.
99.9×9.9=99.9×(10-0.1)=999-9.99=999-10+0.01=989.01 (12.5+2.5)×0.8=12.5×0.8+2.5×0.8=10+2=12
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