---
id: 5900f4e01000cf542c50fff2
challengeType: 5
title: 'Problem 371: Licence plates'
---

## Description
<section id='description'>
Oregon licence plates consist of three letters followed by a three digit number (each digit can be from [0..9]).
While driving to work Seth plays the following game:
Whenever the numbers of two licence plates seen on his trip add to 1000 that's a win.


E.g. MIC-012 and HAN-988 is a win and RYU-500 and SET-500 too. (as long as he sees them in the same trip).


Find the expected number of plates he needs to see for a win.
Give your answer rounded to 8 decimal places behind the decimal point.


Note: We assume that each licence plate seen is equally likely to have any three digit number on it.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler371()</code> should return 40.66368097.
    testString: assert.strictEqual(euler371(), 40.66368097, '<code>euler371()</code> should return 40.66368097.');

```

</section>

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

<div id='js-seed'>

```js
function euler371() {
  // Good luck!
  return true;
}

euler371();
```

</div>



</section>

## Solution
<section id='solution'>

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