freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-72-counting-fractions.english.md

---
id: 5900f3b41000cf542c50fec7
challengeType: 5
title: 'Problem 72: Counting fractions'
---

## Description
<section id='description'>
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.
If we list the set of reduced proper fractions for d ≤ 8 in ascending order of size, we get:
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
It can be seen that there are 21 elements in this set.
How many elements would be contained in the set of reduced proper fractions for d ≤ 1,000,000?
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler72()</code> should return 303963552391.
    testString: assert.strictEqual(euler72(), 303963552391, '<code>euler72()</code> should return 303963552391.');

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function euler72() {
  // Good luck!
  return true;
}

euler72();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```
</section>