---
id: 5900f4e01000cf542c50fff2
title: 'Problem 371: Licence plates'
challengeType: 5
forumTopicId: 302033
dashedName: 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.

# --hints--

`licensePlates()` should return `40.66368097`.

```js
assert.strictEqual(licensePlates(), 40.66368097);
```

# --seed--

## --seed-contents--

```js
function licensePlates() {

  return true;
}

licensePlates();
```

# --solutions--

```js
// solution required
```