题目
The harmonic mean of n numbers is the reciprocal of the arithmetic mean of their reciprocals. What is the harmonic mean of 2, 4, 6, and 12 ?
解析
求\(\left( \frac{1}{2}, \frac{1}{4}, \frac{1}{6}, \frac{1}{12} \right)\)的算术平均数
分母的最小公倍数(LCM)= 12
平均数 = 总和 ÷ 项数
总和 = \(\frac{6+3+2+1}{12} = \frac{12}{12} = 1\)
算术平均数 = \(\frac{1}{4}\)
调和平均数 = \(1 \div (\frac{1}{4}) = 4\)
选项D