问题如下：
A manager invests €5,000 annually in a security for four years at the prices shown in the following table.
The average price paid for the security is closest to:
选项：
A.€76.48.
B.€77.26.
C.€78.00
解释：
A is correct.
The harmonic mean is appropriate for determining the average price per unit. It is calculated by summing the reciprocals of the prices; then averaging that sum by dividing by the number of prices; and finally, taking the reciprocal of the average: 4/[(1/62.00) + (1/76.00) + (1/84.00) + (1/90.00)] = €76.48.
老师，看哪里可以看出使用调和平均数而不是平均数，还有类似题怎么注意
