---
id: 5900f4571000cf542c50ff6a
challengeType: 5
title: 'Problem 235: An Arithmetic Geometric sequence'
forumTopicId: 301879
---
## 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.
## Instructions
## Tests
```yml
tests:
- text: euler235() should return 1.002322108633.
testString: assert.strictEqual(euler235(), 1.002322108633);
```
## Challenge Seed
```js
function euler235() {
// Good luck!
return true;
}
euler235();
```