fix: replace .english.md extension with .md

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-469-empty-chairs.md

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+---
+id: 5900f5411000cf542c510053
+challengeType: 5
+title: 'Problem 469: Empty chairs'
+forumTopicId: 302144
+---
+
+## Description
+<section id='description'>
+In a room N chairs are placed around a round table.
+Knights enter the room one by one and choose at random an available empty chair.
+To have enough elbow room the knights always leave at least one empty chair between each other.
+
+
+When there aren't any suitable chairs left, the fraction C of empty chairs is determined.
+We also define E(N) as the expected value of C.
+We can verify that E(4) = 1/2 and E(6) = 5/9.
+
+
+Find E(1018). Give your answer rounded to fourteen decimal places in the form 0.abcdefghijklmn.
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>euler469()</code> should return 0.56766764161831.
+    testString: assert.strictEqual(euler469(), 0.56766764161831);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function euler469() {
+
+  return true;
+}
+
+euler469();
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+```js
+// solution required
+```
+
+</section>