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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/averages-root-mean-square.md

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+---
+title: Averages/Root mean square
+id: 594da033de4190850b893874
+challengeType: 5
+forumTopicId: 302228
+---
+
+## Description
+<section id='description'>
+Compute the  <a href="https://en.wikipedia.org/wiki/Root mean square" title="wp: Root mean square" target='_blank'>Root mean square</a>  of the numbers 1 through 10 inclusive.
+The <i>root mean square</i> is also known by its initials RMS (or rms), and as the <strong>quadratic mean</strong>.
+The RMS is calculated as the mean of the squares of the numbers, square-rooted:
+<big>$$x_{\mathrm{rms}} = \sqrt {{{x_1}^2 + {x_2}^2 + \cdots + {x_n}^2} \over n}. $$</big>
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>rms</code> should be a function.
+    testString: assert(typeof rms === '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);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function rms(arr) {
+
+}
+```
+
+</div>
+
+
+### After Test
+<div id='js-teardown'>
+
+```js
+const arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+const answer1 = 6.2048368229954285;
+```
+
+</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>