When did people first start to send Christmas cards? The first cards carrying messages of goodwill to friends at Christmas were sent in the 19th century in Britain.

An edition of 1,000 cards bearing an image of a family gathering and the message 'A Merry Christmas and a Happy New Year to you' went on sale in London in 1843.

The custom of sending Christmas cards caught on in the United States in the 1870s.

Who invented mathematics? TOMATO Delia Memorial School (Hip Wo) Mathematics was used by many ancient civilisations including the Mesopotamians, Egyptians, Greeks and Chinese. It was also extensively studied by Islamic scholars from the 9th to 15th centuries. Although the ancients laid important foundations, most of the major developments in mathematics came after the 15th century along with other scientific discoveries.

The Mesopotamian civilisation, which covered much of modern- day Iraq, left behind clay tablets which show it had a versatile numerical system about 4,000 years ago. They solved problems by methods similar to the algebra used today. They knew about the relationship of the hypotenuse and the other two sides of a right-angled triangle - now commonly known as Pythagoras' theorem - more than 1,000 years before Greek mathematician Pythagoras.

The ancient Greeks had two main branches of maths which developed out of practical necessity: geometry - literally the measurement of land - and arithmetic which developed as trade with Phoenician merchants flourished.

Although not the first to use mathematics, the Greeks could be said to have invented it because they developed it as a theoretical discipline. They used mathematical statements to represent general principles and developed the concept of having to confirm statements with proof.