数学题：一根电线，第一次剪下2/5（五分之二），又接上18米，这样比原来长20%（百分之二十）。这根铁丝原来长几米？（18米就是全长的五分之二与全长的百分之二十的米数之和）

数学题解答：18÷（2/5　+　20%）＝30（米）

答：这根铁丝原来长30米。

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