Since **1840**, when the 'Penny Post' was introduced by
*Rowland Hill*, there have been many changes in the Postal Service,
and in recent years many technological advances.

Much of the mail is now automatically sorted. Of particular importance has
been the introduction of **Postcodes**, which were started in **1966**
and now cover the whole of the UK.

This alpha-numeric system, made up of between 5 and 7 numbers and letters, was firstly used in order to divide the whole country efficiently and effectively into

**AREAS DISTRICTS SECTORS UNITS**

but secondly because people can remember a mixture of numbers and letters more easily than, for example, just numbers. Do you think this is true? Here is a typical postcode.

**Problem 1** **a)** What is the **maximum** number of AREAS
possible using postcodes of this form?

** b)**
For each Area, how many DISTRICTS could there be?

** c)**
For each District, how many SECTORS are possible?

** d)**
For each Sector, how many UNITS are possible?

**Problem 2 a)** Using your answers to Problem 1, how many UNITS
could there be in the whole country?

** b)**
There are about **24 million** households and business addresses in the
UK. Could each one have a unique postcode?

In fact the Post Office uses

**120 Areas 2,900 Districts 9,000 Sectors 2,000,000
Units.**

**Problem 3 a)** On average, how many Districts per Area are used?

**b)**
How many Sectors per District are used?

**c)**
How many Units per Sector are used?

**
d)** How many households/businesses are there per Unit?

**Problem 4** Why do you think the Post Office
does **not** identify each address with a unique postcode?

**EXTENSION** Obtain you local postcodes from your nearest main Post Office.
Illustrate the DIstricts, Sectors and Units on a local map.