请问【费费数学】第一部分23题？

frankliny

23、两个班a，b，在某次考试中的分数如下：问a和b在一起的average>median ? 班级    median score     average score
  a           80              82  
  b           78              74

（1）a 37人，b40人；
（2）a+b 77人；



a37-->a(19)=80-->19 ps >=80
b40-->b(21)=78--->20 ps >=79 --->median(a+b)=(a+b)39>79 which is more than the ave(a+b) around 78
选a





b为什么不对呢？我觉得条件（2）a+b ＝77人无论如何算median都>average？

fox123456

Here is my take:

We need the average of both sets, which is 77.8 in this case.
If we tweak the ratio between the number of each set and the number of total students.
Let's say, set A 60 students
              set B 17 students
The average would become 80.234
Then the line below would not be valid:
median(a+b)=(a+b)39>79 which is more than the ave(a+b) around 78
Hence, we need to choose a) and b) itself is not sufficient

lianlonger

a+b=77，若a的人数为1，b的人数为76，average>median ？