freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-235-an-arithmetic-geometric-sequence.english.md

---
id: 5900f4571000cf542c50ff6a
challengeType: 5
title: 'Problem 235: An Arithmetic Geometric sequence'
---

## Description
<section id='description'>
Given is the arithmetic-geometric sequence u(k) = (900-3k)rk-1.
Let s(n) = Σk=1...nu(k).


Find the value of r for which s(5000) = -600,000,000,000.


Give your answer rounded to 12 places behind the decimal point.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler235()</code> should return 1.002322108633.
    testString: assert.strictEqual(euler235(), 1.002322108633, '<code>euler235()</code> should return 1.002322108633.');

```

</section>

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

<div id='js-seed'>

```js
function euler235() {
  // Good luck!
  return true;
}

euler235();
```

</div>



</section>

## Solution
<section id='solution'>

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