Exercise

# Harmonic mean

The harmonic mean is the reciprocal of the arithmetic mean of the reciprocal of the data. That is

$$ \text{harmonic_mean}(x) = 1 / \text{arithmetic_mean}(1 / x) $$

The harmonic mean is often used to average ratio data. You'll be using it on the price/earnings ratio of stocks in the Standard and Poor's 500 index, provided as `std_and_poor500`

. Price/earnings ratio is a measure of how expensive a stock is.

The `dplyr`

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Instructions 1/3

**undefined XP**

*Look at*Write a function,`std_and_poor500`

(you'll need this later).`get_reciprocal`

, to get the reciprocal of an input`x`

. Its only argument should be`x`

, and it should return one over`x`

.