求助og数学绿皮书P81，第148题~~~~~

amandayueyue

有三个图，不容易上图，直接上题了...不明白每个图怎么确定平均值的，希望有做到的帮助解答下哦....谢谢啦
if the variables, X,Y and Z take on only the values 10,20,30,40,50,60 or 70 with frequencies indicated by the shaded regions above, for which of the frequency distributions is the mean equal to the median?
正确答案是E.    X and Z