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脱式计算，能简算的要简算．1.22×3.8+3.8×8.78 13.28-7.69-0.31 +++ 3.8÷（12.4÷3.1）+0.5 24-6+-2 -++．

给得数点上小数点．4.2×3.8=1596 7.45×1.3=9685 2.15×4.2=90302.06×13=2678 5.3×4.2=2226 0.37×0.15=555．

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