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。

推荐阅读：
7 Ways to Use Video on Your Blog to Get More Engagement　 Should You Build Your Blog on a CMS or a Website Builder?　 5 Top Tips on How to Be a Top Game Blogger　 Blog Stalkers: Staying Safe Online　 How Social Media Paid Ads Can Boost Blog Post Promotion　 Are You Focused Enough To Freelance? 4 Tips For Bloggers　 The Secure Shell (SSH) Chrome Extension developed by Google　 The Valid Mountain Array Algorithm　 Recovery Models in SQL Server　 The Algorithm to Construct the Rectangle Given Its Area