2018-09-30 22:01:58 +00:00
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---
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id: 5900f3b41000cf542c50fec7
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challengeType: 5
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title: 'Problem 72: Counting fractions'
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---
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## Description
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<section id='description'>
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Consider the fraction, n/d, where n and d are positive integers. If n<d and HCF(n,d)=1, it is called a reduced proper fraction.
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If we list the set of reduced proper fractions for d ≤ 8 in ascending order of size, we get:
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1/8, 1/7, 1/6, 1/5, 1/4, 2/7, 1/3, 3/8, 2/5, 3/7, 1/2, 4/7, 3/5, 5/8, 2/3, 5/7, 3/4, 4/5, 5/6, 6/7, 7/8
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It can be seen that there are 21 elements in this set.
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How many elements would be contained in the set of reduced proper fractions for d ≤ 1,000,000?
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</section>
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## Instructions
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<section id='instructions'>
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</section>
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## Tests
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<section id='tests'>
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```yml
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2018-10-04 13:37:37 +00:00
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tests:
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- text: <code>euler72()</code> should return 303963552391.
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2018-10-08 00:01:53 +00:00
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testString: 'assert.strictEqual(euler72(), 303963552391, "<code>euler72()</code> should return 303963552391.");'
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2018-09-30 22:01:58 +00:00
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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function euler72() {
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// Good luck!
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return true;
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}
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euler72();
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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