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           ☆1 inequalities

[ 1/1Inequality]
    Assignment:Find the solution set of inequality (60－50)×a+(60×0.9－50)×(40－a)+(70－60)×40 ≥680 .
    Question type: Inequality
    Solution:
    The inequality can be reduced to 1 inequality：
         ( 60 - 50 ) × a + ( 60 × 0.9 - 50 ) × ( 40 - a ) + ( 70 - 60 ) × 40 ≥680         (1)

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    From inequality(1)：
         a ≥ 20

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    The final solution set is :
         a ≥ 20

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