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Pi
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Pi

The Greek letter π (transliterated into English as pi) is used to denote one of the most famous constants in mathematics: the ratio between the diameter and circumference of a circle. It's what's known as an irrational number, because it can't be expressed as a ratio (i.e. a fraction). For this reason, it is impossible to give an exact value for pi; all we can do is give an approximation.

At school we were taught (or we were in my day) that the fraction 22/7, or three and one seventh, gives a close approximation to pi. This is a rational number, because it can be expressed as a ratio, but like pi it can't be written down exactly as a decimal fraction, because its digits repeat (or recur, as the mathematicians say) ad infinitum. It's equal to approximately 3.142857; after this, those six digits (the ones after the decimal place) recur.

The actual value of pi, to 31 decimal places, is 3.1415926535897932384626433832795.

It's always useful to know the first few digits of pi, but unless you're a memory expert (in a way that a quizzer isn't necessarily) you'll probably need a mnemonic.

There are various mnemonics, and most if not all of them involve learning a sentence or verse where the number of letters in each word in turn gives you the requisite digits.

Here's one I learnt from BBC Radio 4's Brain of Britain, some years ago, which gives the first eight digits (including the one before the decimal point):

May I have a large container of coffee?

This has always been enough for me in any quiz where the subject (of the value of pi) has ever come up.

Mathematicians will notice that it's not strictly correct, because if we were giving the value of pi to eight significant figures, or seven decimal places, the eighth digit should be a 7 and not a 6.

If you'd like to see a mnemonic for more digits of pi, I would refer you to i before e (except after c), by Judy Parkinson (Michael O'Mara Books Ltd, London, 2007). Subtitled Old-School Ways to Remember Stuff, this book is all about mnemonics, and it gives various examples for pi – including one that gives you the 31 digits as above. It stops at 31 because (as Ms. Parkinson herself points out) the 32nd decimal place is occupied by a zero, which can't easily be covered by the method of counting the number of letters in words.

You will also find several other mnemonics in Ms. Parkinson's book which I've stolen for this website.

Other

The questions in this section have nothing in common, except that in each case, the answer is a number.

Where a number is followed by an ellipsis (...), this means that the value given here is approximate.

Square root of 0.25 Click to show or hide the answer
Surfaces on a Mobius strip Click to show or hide the answer
Square root of 2 Click to show or hide the answer
The 'golden ratio' (known to mathematicians as phi) Click to show or hide the answer
The only even prime number; also the lowest (1 no longer qualifies) Click to show or hide the answer
The base of natural logarithms (e) – a.k.a. Euler's number or Napier's constant Click to show or hide the answer
Hearts of an octopus Click to show or hide the answer
Spots on the Domino's Pizza logo Click for more information
Pi (see previous section for more) Click to show or hide the answer
Compartments in the stomach of a cow Click to show or hide the answer
Horses involved in the bet known as a Yankee
Lines in a clerihew
Arms of a starfish Click to show or hide the answer
Halogens (naturally occurring)
Lines in a limerick
Sides of a prism
Number of places (in each of which there may or may not be a dot) in the cell, or grid, used to represent a character in Braille Click for more information Click to show or hide the answer
Pips in the Greenwich Time Signal (the last one is a long one)
Points on a snowflake
Points on the Star of David
Wings of a Seraph
Hills of Rome Click to show or hide the answer
Opposite sides of a die add up to
Points on the Statue of Liberty's crown
Sides on a 50p piece
Neutral on the pH scale Click to show or hide the answer
Bits in a byte (always, in quizzes!) Click to show or hide the answer
Corners on a cube
Humans (traditionally) on Noah's Ark
Nails in a horseshoe (normally)
Points on a Maltese Cross
Records allowed on Desert Island Discs
Queen Victoria's children Click to show or hide the answer
Gates in the Thames Flood Barrier Click to show or hide the answer
Legs on a lobster
Tentacles of a squid
Herbs & spices used in KFC's secret recipe Click for more information Click to show or hide the answer
Confederate states
Branches on the antlers of a male stag (minimum) Click to show or hide the answer
Labours of Hercules
Tribes of Israel
Avenues that radiate from the Place Charles de Gaulle (Paris – previously, and sometimes still, known as the Place de l'Etoile)
Baker's dozen Click to show or hide the answer
People at the Last Supper
US colonies (states) that declared independence in 1776, and hence stripes on the US flag
Witches in a coven
Enigma variations (Elgar) Click to show or hide the answer
Lines in a sonnet
Stations of the Cross
Degrees of longitude in a time zone Click to show or hide the answer
People on a jury, in Scotland
Stones per player at the start of a game of Backgammon
Annas in a rupee Click to show or hide the answer
Syllables in a haiku Click to show or hide the answer
Quires in a ream Click to show or hide the answer
Shillings in a guinea (prior to 1971) Click to show or hide the answer
Spots on a die
Letters (characters) in the Hebrew alphabet Click to show or hide the answer
Pairs of chromosomes in each human cell Click to show or hide the answer
Letters in the Greek alphabet Click to show or hide the answer
Pieces at the start of a game of draughts
Sheets in a quire Click to show or hide the answer
Counties in the Republic of Ireland Click to show or hide the answer
Cantons in Switzerland
EU member states (the latest to join was Croatia in 2013) Click to show or hide the answer
Characters in the Arabian alphabet
Pieces in a set of dominoes
The Chatanooga Choo Choo left on track number Click to show or hide the answer
Letters in the Russian alphabet Click to show or hide the answer
Pieces in a chess set Click to show or hide the answer
Points of the compass
Boroughs in Greater London (not counting the City of London)
Pods on the London Eye
Numbers on a roulette wheel (European – including French and British) Click to show or hide the answer
Numbers on a roulette wheel (American) Click to show or hide the answer
Strings on a harp Click to show or hide the answer
Original members (1945) of the United Nations Click to show or hide the answer
Countries in the Commonwealth Click to show or hide the answer
Small squares on a Rubik cube Click to show or hide the answer
Letters in Llanfairpwllgwyngyllgogeryllwyndrobwyllllantisiliogogogoch Click to show or hide the answer
'The Brighton Line' (in what Bob Monkhouse used to call "Bingo lingo") Click to show or hide the answer
Squares on a chess (or draughts) board Click to show or hide the answer
Cards in a Tarot pack Click to show or hide the answer
Small squares (into each of which you write a number) on a Su Doku grid Click to show or hide the answer
Keys on a standard piano Click to show or hide the answer
The highest number in bingo (standard version) Click to show or hide the answer
Theses in Martin Luther's Disputation on the Power and Efficacy of Indulgences (1517) Click to show or hide the answer
Room that contains "the worst thing in the world" (i.e. whatever the victim is most afraid of) in George Orwell's Nineteen Eighty–Four Click to show or hide the answer
Floors in the Empire State Building Click to show or hide the answer
A supercentenarian is someone who is over ... years old Click to show or hide the answer
Emergency phone number, in the EU and several other countries – standardised by the EU Council in 1991, reaffirmed in 2002 Click to show or hide the answer
Elements in the Periodic Table (the last four being officially named in 2016) Click to show or hide the answer
Tiles in Mah Jongg (Western version) Click to show or hide the answer
Hours in a week Click to show or hide the answer
Spots on a set of (double six) dominoes Click to show or hide the answer
Number for the UK's Directory Enquiries service, operated exclusively by British Telecom until 2002 Click to show or hide the answer
Pennies in a pound (pre–1971) Click to show or hide the answer
Squares on a Scrabble board Click to show or hide the answer
Sheets in a ream Click to show or hide the answer
Total of all the numbers on a roulette wheel Click to show or hide the answer
Arabian Nights Click to show or hide the answer
Bytes in a kilobyte Click to show or hide the answer
Bytes in a megabyte Click to show or hide the answer

© Haydn Thompson 2017–21