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# We define the harmonic mean of a set of numbers as the reciprocal of

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Re: We define the harmonic mean of a set of numbers as the reciprocal of [#permalink]
MathRevolution wrote:
[GMAT math practice question]

We define the harmonic mean of a set of numbers as the reciprocal of the average (arithmetic mean) of the reciprocals of the numbers. What is the harmonic mean of 20 and 30?

A. 22
B. 24
C. 25
D. 26
E. 28

(1/20 + 1/30)/2 = 5/60 = 1/12*2, average of this

Reciprocal of this term = 24

B
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Re: We define the harmonic mean of a set of numbers as the reciprocal of [#permalink]
=>

$$1 / { ( \frac{1}{20} + \frac{1}{30} ) / 2 } = 1 / { ( \frac{3}{60} + \frac{2}{60} ) / 2 } = 1 / { (\frac{5}{60}) / 2 } = 1 / { \frac{5}{120} } = \frac{120}{5} = 24.$$

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Re: We define the harmonic mean of a set of numbers as the reciprocal of [#permalink]
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Re: We define the harmonic mean of a set of numbers as the reciprocal of [#permalink]
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