例１.甲、乙、丙、丁与小强五位同学一起比赛象棋，每两人都要赛一盘。到现在为止，甲已经赛了四盘，乙赛了三盘，丙赛了两盘，丁赛了一盘。

问：小强赛了几盘？

推荐阅读：
A Blogger’s Guide to Successful Content Marketing in a Saturated　 6 Remote Jobs For Supplemental Income　 5 Tips When Preparing for a Business Conference　 Customizing WordPress with Branda by WPMU DEV　 How to Blog Like Shakespeare　 Depth First Search Algorithm to Delete Insufficient Nodes in Roo　 C/C++ Program to Compute the Angle Between Hands of a Clock　 What Should Your Anti Virus Software Have in Order to Be Effecti　 The Importance of SEO and How They Improve the Number of Your Cl　 Learn The Basics Of Google My Business