数学题:一种商品随季节出售，如果按售价降低10%，任可盈利200元，如果降价20%，则亏损220元。这件商品原价是多少元？

数学题解答：降价10%和降价20%，这两种情况相差了原价的：20% – 10% = 10%

而盈利200元和亏损220元，一正一反相差了：200 + 220 = 420（元）

这420元即相当于原价的10%，所以原价是：

420 ÷ 10% = 4200（元）

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