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Science, Maths & Technology

10 facts about the number ten

Updated Sunday 10th April 2016

OpenLearn is 10 this year, so to mark this occasion we're taking a look at 10 facts on our age. 

1: Crabs have 10 legs

Crabs belong to a group of animals called decapods, meaning 'ten-footed'. They use their first pair of legs (or claws) for defence or to capture food - you wouldn't want to be pinched by these blighters! The other four pairs of legs are primarily for walking; one set of legs leads and the other follows which is why they walk sideways. 

  • Like animals? Find out more about the first appearance of major groups of invertebrates and vertebrates, and the invasion of the land in our free course: Life in the Palaeozoic.

2: 10 seconds determines a 'knockout' in boxing

A KO is something the likes of Tyson Fury would rather give than receive. During a fight, when a boxer falls to the floor the referee must count to 10 to determine whether they are able to get back up to continue.  If not, their opponent wins by knockout. 

  • Explore the changing face of sport in the lives of Muslim women and their surprising uptake of boxing in this article: Muslim women and sport.

3: The Korean alphabet has 10 vowels

Copyright free image Icon Copyright free: By photo by Kbarends (cropped from en:Image:Hunminjeongeumhaerye.jpg) [Public domain], via Wikimedia Commons

Hangeul (as it is called in South Korea) is the Korean alphabet. It was created in 1443 by Sejong, the fourth king of the Yi Dynasty. The Korean alphabet consists of a whopping 40 letters, including compounds: 10 pure vowels, 11 compound vowels, 14 basic consonants, and 5 double consonants. 

  • While we don't offer a free course in Korean, try out a free course on the language of one of Korea's neighbouring countries, China, with Beginners' Chinese.

4: Number 10 is where the British Prime Minister lives

10 Downing Street Creative commons image Icon Photo: Sergeant Tom Robinson RLC/MOD [OGL], via Wikimedia Commons under Creative-Commons license

10 Downing Street has been the official residence and the office of the British Prime Minister since 1735. Number 10 has 3 functions: it is the home of the British Prime Minister, it is their office, and it is also the place where the Prime Minister entertains guests from The Queen to other world leaders. It's supposedly a bit like Doctor Who's Tardis and the Spice Bus from the Spice World: deceptively large on the inside.

  • Ever wondered how you can boot a Prime Minister out of Number Ten? Check out Andrew Rawnsley's video guide to Sacking Prime Ministers.

5: 10 was a sacred number to Pythagoras

Copyright free image Icon Copyright free: By Andargor at English Wikipedia (Transferred from en.wikipedia to Commons.) [Public domain], via Wikimedia Commons

Pythagoras (the guy who thousands of children curse every day in maths lessons) and his followers thought that 10 the most sacred number of all, because 1 + 2 + 3 + 4 = 10. The numbers represent the following: (1) existence, (2) creation, (3) life and (4) the elements earth, air, fire and water.

6: Canada has 10 provinces

Canada is the second largest country in the world, by land mass, and consists of 10 provinces: Alberta, British Columbia, Manitoba, New Brunswick, Newfoundland and Labrador, Nova Scotia, Ontario, Prince Edward Island, Quebec, and Saskatchewan. 

7: The Ten Commandments are crucial to Judaism and Christianity

The Ten Commandments, are described in the Bible as having been given to the Israelites by God at Mount Sinai. The commandments instruct to worship only God, to honour parents, and to keep the Sabbath holy; as well as forbidding idolatry, blasphemy, murder, adultery, theft, dishonesty, and coveting. Some are essential to our laws today; others - not so much (Sunday trading hours, anybody?). 

  • Think this is interesting? Dig deeper into various religions with our free course: Studying religion

8: The word 'decimate' stems from the number 10

This word is often misused as a synonym for ‘destroy’ but the correct meaning of the verb ‘to decimate’ is ‘to reduce by a 10th'. This can be traced back to ancient Rome where the killing of one in ten soldiers in a cohort was the brutal punishment for cowardice or mutiny. Who said Romans were blood-thirsty? 

  • Go on a journey with one of the Roman Empire's most famous and well-travelled Emperors, Hadrian, in our game: Hadrian: The Roamin' Emperor.

9: The interval of a major tenth is an octave plus a major third

In music and music theory, a tenth is the term we use to define (a) the note ten scale degrees from the root of a chord and (b) the interval between the root and the tenth. The two are also called the median and a compound third, respectively. Confusing, huh? 

10: The atomic number of neon

Creative commons image Icon By Alchemist-hp (talk) ( (Own work) [GFDL 1.2], via Wikimedia Commons under Creative-Commons license

Walter White and other chemistry whizzes know that Neon is a chemical element with atomic number 10 and symbol Ne. The colourless and odourless gas sits in group 18 of the periodic table with the noble gases. The name neon is derived from the Greek word, νέον, meaning new.

  • Explore the impact of chemical elements on our bodies, our world, and see how they changed the course of history in this interactive: Elements of the Periodic table

The Open University launched OpenLearn, a website dubbed 'The home of free learning', in October 2006 and since then it has gained over 40 million unique users and won awards recognising its array of valuable free learning content.
To celebrate OpenLearn's 10th anniversary, we are releasing a new listicle centralised round the number 10 on the 10th of every month in the 10 month lead up to October. Check out our Ten Years of OpenLearn hub to enjoy even more free learning!





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