99.9×9.99 简便计算

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99.9×9.99 简便计算

99.9×9.99
=(100-0.1)×9.99
=100×9.99-0.1×9.99
=999-0.999
=998.001
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=999*999/1000
=(1000-1)^2 /1000

原式=(100-0.1)×9.99
=100×9.99-0.1×9.99
=999-0.999
=998.001

=(100-0.1)×(10-0.01)=1000-1-1+0.001=998.001