---
id: 5900f4411000cf542c50ff54
challengeType: 5
title: 'Problem 213: Flea Circus'
---

## Description
<section id='description'>
A 30×30 grid of squares contains 900 fleas, initially one flea per square.
When a bell is rung, each flea jumps to an adjacent square at random (usually 4 possibilities, except for fleas on the edge of the grid or at the corners).

What is the expected number of unoccupied squares after 50 rings of the bell? Give your answer rounded to six decimal places.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler213()</code> should return 330.721154.
    testString: assert.strictEqual(euler213(), 330.721154, '<code>euler213()</code> should return 330.721154.');

```

</section>

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

<div id='js-seed'>

```js
function euler213() {
  // Good luck!
  return true;
}

euler213();
```

</div>



</section>

## Solution
<section id='solution'>

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