fix: replace .english.md extension with .md

curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-31-coin-sums.md

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+---
+id: 5900f38b1000cf542c50fe9e
+challengeType: 5
+title: 'Problem 31: Coin sums'
+forumTopicId: 301965
+---
+
+## Description
+<section id='description'>
+
+In England the currency is made up of pound, £, and pence, p, and there are eight coins in general circulation:
+
+<div style='margin-left: 4em;'>1p, 2p, 5p, 10p, 20p, 50p, £1 (100p) and £2 (200p).</div>
+
+It is possible to make £2 in the following way:
+
+<div style='margin-left: 4em;'>1×£1 + 1×50p + 2×20p + 1×5p + 1×2p + 3×1p</div>
+
+How many different ways can `n` pence be made using any number of coins?
+
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>coinSums(50)</code> should return a number.
+    testString: assert(typeof coinSums(50) === 'number');
+  - text: <code>coinSums(50)</code> should return 451.
+    testString: assert(coinSums(50) == 451);
+  - text: <code>coinSums(100)</code> should return 4563.
+    testString: assert(coinSums(100) == 4563);
+  - text: <code>coinSums(150)</code> should return 21873.
+    testString: assert(coinSums(150) == 21873);
+  - text: <code>coinSums(200)</code> should return 73682.
+    testString: assert(coinSums(200) == 73682);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function coinSums(n) {
+
+  return n;
+}
+
+coinSums(200);
+```
+
+</div>
+
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+const coinSums = (n) => {
+  const getWays = (n, m=8, c=[1, 2, 5, 10, 20, 50, 100, 200]) => {
+    if (n === 0) return 1;
+    if (m === 0 || n < 0) return 0;
+    return getWays(n - c[m - 1], m, c) + getWays(n, m - 1, c);
+  };
+  return getWays(n);
+};
+```
+
+</section>