提问三道数学题1.S is a set of n consecutive integers.比较the mean of

提问三道数学题
1.S is a set of n consecutive integers.比较the mean of S与the median of S大小 答案是一样大
我知道Mean=(a1+an)/2,当n=2k时,median=(ak+ak+1)/2；当n=2k+1时,median=ak+1,问题是怎么比较出mean和median想等的?（n,k,k+1均为a的角标）
2.If 9 trees are originally planted in a
circular pattern(就是9个点围成一个圆圈),what is the least number of trees that
must be transplanted so that the 9 trees will be in 2 straight rows?
咋做?答案是9-2*2=5,这是啥意思?（此题的图无法上传,若实在不明题意,就不必回答）
3.A rectangular rug covers half of a
rectangular floor that is 9 feet wide and 12 feet long.If the dimensions of the
rug are in the same ratio as those of the floor,how many feet long is the rug?答案是6根号下2
请问既然rug盖住floor一半,为何不能认为其长或宽是floor的一半?而是非要通过面积一半来算?