30%x+(x-30%x)80%+70=x X-30%X-80%（X-30%X）=70

题目

30%x+(x-30%x)80%+70=x X-30%X-80%（X-30%X）=70
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答案

x-30%x-(x-30%x)80%=70
x-30%x-70%x*80%=70
x-30%x-56%x=70
70%x-56%x=70
14%x=70
x=500