---
id: 5900f4e01000cf542c50fff2
challengeType: 5
title: 'Problem 371: Licence plates'
---
## 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.
## Instructions
## Tests
```yml
tests:
- text: euler371() should return 40.66368097.
testString: assert.strictEqual(euler371(), 40.66368097, 'euler371() should return 40.66368097.');
```
## Challenge Seed
```js
function euler371() {
// Good luck!
return true;
}
euler371();
```