2018-09-30 22:01:58 +00:00
---
title: Averages-Root mean square
id: 594da033de4190850b893874
challengeType: 5
---
## Description
< section id = 'description' >
< p > Compute the < a href = "https://en.wikipedia.org/wiki/Root mean square" title = "wp: Root mean square" > Root mean square< / a > of the numbers 1 through 10 inclusive.< / p >
< p > The root mean square is also known by its initials RMS (or rms), and as the quadratic mean.< / p > < p > The RMS is calculated as the mean of the squares of the numbers, square-rooted:< / p >
< p >< big > $$x_{\mathrm{rms}} = \sqrt {{{x_1}^2 + {x_2}^2 + \cdots + {x_n}^2} \over n}. $$</ big ></ p >
< / section >
## Instructions
< section id = 'instructions' >
< / section >
## Tests
< section id = 'tests' >
```yml
2018-10-04 13:37:37 +00:00
tests:
- text: < code > rms</ code > is a function.
2018-10-20 18:02:47 +00:00
testString: assert(typeof rms === 'function', '< code > rms< / code > is a function.');
- text: < code > rms([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])</ code > should equal < code > 6.2048368229954285</ code > .
testString: assert.equal(rms(arr1), answer1, '< code > rms([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])< / code > should equal < code > 6.2048368229954285< / code > .');
2018-09-30 22:01:58 +00:00
```
< / section >
## Challenge Seed
< section id = 'challengeSeed' >
< div id = 'js-seed' >
```js
function rms (arr) {
// Good luck!
}
```
< / div >
### After Test
< div id = 'js-teardown' >
```js
2018-10-20 18:02:47 +00:00
const arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const answer1 = 6.2048368229954285;
2018-09-30 22:01:58 +00:00
```
< / div >
< / section >
## Solution
< section id = 'solution' >
```js
function rms (arr) {
const sumOfSquares = arr.reduce((s, x) => s + x * x, 0);
return Math.sqrt(sumOfSquares / arr.length);
}
```
< / section >