问题如下:
Peter bought a security for $55 in year 1, $60 in year 2, $64 in year 3, $70 in year 4. The harmonic mean of the price will be:
选项:
A. 61.77.
B. 25.
C. 37.04
解释:
A is correct. The harmonic mean : 4/[(1/55) + (1/60) + (1/64) + (1/70)] = 61.77
调和平均数的公式可以列出来,可是怎么计算啊,有好的计算方法吗?我硬算了几遍都是错的