50 Fun Facts About Elementary School Math

Which symbol did Welshman Robert Recorde invent in 1557 to avoid 'the tedious repetition' of a three-word phrase?

The equals sign replaced the words 'is equal to', which Recorde was tired of writing out, and he chose two lines 'because no two things can be more equal'.

Which number, a 1 followed by a hundred zeros, got its name in 1920 from a nine-year-old boy?

Googol was the word Milton Sirotta offered his uncle, mathematician Edward Kasner, and an intentional misspelling of it later became the name of the search engine Google.

What is 7 times 8, the question UK Chancellor George Osborne refused to answer from a schoolboy on Sky News?

7 × 8 = 56, and Osborne, who said he had studied maths at A-level, replied that he had 'made it a rule in life not to answer' maths questions.

How many squares does a standard chessboard have, laid out as eight rows of eight with the colours alternating?

A chessboard has 64 squares, and a games book of 1283 argued that eight by eight was the ideal size because a 10×10 board made chess too tiresome and 6×6 too quick.

How many sides does a red stop sign have, a shape chosen so drivers can recognise it from the back?

A stop sign has 8 sides, and the octagon was standardised in 1922 partly because its outline could be recognised at night before signs were reflective.

How many loaves make a baker's dozen, the extra one added so bakers were not punished for short weight?

A baker's dozen is 13, because a baker caught selling underweight bread could be fined, flogged or have the oven destroyed, so a spare loaf was cheap insurance.

What do the three inside angles of any triangle on flat paper add up to, the same as a straight line?

Triangle angles total 180° only on a flat surface; on a curved surface such as the Earth's, the three angles add up to more, as much as 540°.

Which date is Pi Day, chosen because of the way the United States writes the month before the day?

March 14 is 3/14 in US month-day order, pi's first three digits; Albert Einstein was born that day, and July 22 (22/7) is Pi Approximation Day.

Which shape do honeybees build every cell of a honeycomb in, because it fills a surface using the least wax?

Hexagon cells tile a flat surface with less wax than any other equal-cell shape, and the finished comb gains strength under compression.

Which name, from a Latin word meaning 'namer', does the bottom number of a fraction go by?

The denominator 'names' the kind of part, such as halves, thirds or quarters, while the top number, the numerator, from the Latin for 'counter', counts how many of them there are.

Which number does the Roman numeral L stand for, the letter that sits between X and C in value?

L is 50, though on tombstones the Romans occasionally carved 50 as XXXXX, and the largest number the standard seven letters can write is 3,999, MMMCMXCIX.

How many items are in a gross, the old trade count that means a dozen dozens?

A gross is 144, from 12 × 12, and the word comes from the Old French grosse douzaine, a 'large dozen'; a great gross, a dozen gross, is 1,728.

How many years is 'four score and seven', the span Abraham Lincoln counted back to 1776 at Gettysburg?

Four score and seven is 87, a score being 20, and Lincoln spoke in November 1863, 87 years after the Declaration of Independence, perhaps echoing the 'threescore years and ten' of Psalm 90.

Which US coin is the smallest and thinnest in circulation, despite being worth more than a penny or a nickel?

The dime is 17.91 mm across and 1.35 mm thick, smaller than a penny worth a tenth as much, and its name comes from the Old French disme, a 'tenth part'.

Which name, from the Greek for a sharpened stick, does the ÷ division sign go by?

The obelus was first printed as a division sign by Swiss mathematician Johann Rahn in 1659; ancient scholars had used the same mark to flag suspect passages in manuscripts.

When 47 balloons are shared equally among 6 children, how many balloons are left over?

6 × 7 = 42 and 47 − 42 = 5, so 5 balloons are left over; the 'left over' amount is what mathematicians call the remainder, whether dividing numbers or polynomials.

Which clear plastic half-circle, marked in degrees along its curved edge, do pupils use to measure angles?

A protractor is a clear half-disc marked from 0° to 180°, usually with two scales running in opposite directions so an angle can be read from either side; bevel protractors add a pivoting arm for toolmakers.

How many full weeks are in a year, leaving one spare day, or two in a leap year?

A year is 52 weeks plus one day, which is why any date's day of the week moves forward by one each year, or by two once a leap day has passed.

At how many degrees Fahrenheit does water freeze, on the scale the United States still uses for its weather forecasts?

Water freezes at 32 °F and boils at 212 °F; Fahrenheit based the bottom of his scale on the coldest brine mixture he could make and put body heat at 96 degrees.

Which drawing of overlapping circles, invented by an English logician in 1880, shows what two groups have in common?

Venn diagram circles are named for John Venn, whose Cambridge college, Gonville and Caius, honours him with a stained-glass window showing one.

Which graph, first published by William Playfair in 1801, shows how a whole splits into parts as slices of a circle?

The pie chart owes much of its popularity to Florence Nightingale, who adapted it into her 'rose diagram' of 1858 to show Queen Victoria what was killing soldiers in army hospitals.

Which Chinese puzzle cuts a square into five triangles, a square and a parallelogram to rearrange into pictures?

Tangram pieces are called tans, and the craze reached Europe and America on trading ships soon after 1800, with sets made from wood, glass and tortoiseshell.

Which word, one that also means 'blunt', describes an angle between a right angle and a straight line in size?

Obtuse angles sit between a right angle and a straight angle; a smaller angle is acute, and one wider than a straight line but short of a full turn is reflex.

Which triangle, named from Greek words for 'equal' and 'leg', has exactly two sides of the same length?

Isosceles triangles also have two equal angles, a result so early in Euclid that it was nicknamed the pons asinorum, the 'bridge of asses', for sorting students who could follow geometry from those who could not.

Which solid shape, every surface point the same distance from its centre, lets balls roll smoothly in any direction?

A sphere has the smallest surface of any shape enclosing a given volume, which is why bubbles and planets take the form; the name comes from the Greek sphaira, 'ball'.

Which family name, from the Latin for 'four sides', covers squares, rectangles, kites and trapeziums alike?

Quadrilateral comes from quadri and latus, and the Greek-built alternative, tetragon, never caught on the way the Greek names for other many-sided shapes did.

Which word describes the total every time two odd numbers are added, as in 3 + 5 or 7 + 9?

Even is the only possibility, because each odd number is an even one plus 1 and the two spare 1s pair up; odd times odd, by contrast, stays odd.

Which bead-and-rod counting frame is still taught in Japanese primary schools as a way to speed up mental arithmetic?

The abacus in Japan is the soroban, and counting frames go back to Sumer around 2700 BC, lasting until handheld calculators largely replaced them in the 1980s.

Which kind of number word, such as 'third' or 'tenth', tells you position in a line rather than how many?

Ordinal numerals rank things, whereas cardinal numerals such as 'three' count them; English builds most ordinals by changing only the last word, so 523 becomes 'five hundred twenty-third'.

How many degrees are in a right angle, the corner carpenters check with the 3-4-5 rule?

A right angle is 90°, a quarter turn, and a triangle with sides of 3, 4 and 5 units always contains one, a check builders and masons have relied on since antiquity.

How many degrees make a full turn, a count one theory links to the number of days in an ancient year?

A full turn is 360° and the Persian and Babylonian calendars used 360-day years; the Babylonians also counted in sixties, which divide 360 neatly.

How many parts make up the whole in a percentage, a word from the Latin per centum?

Percent means 'by the hundred', so 100 is the whole, and the % sign itself is a worn-down scribble of the Italian per cento.

How many days are in a leap year, the extra one covering the six hours a 365-day year falls short?

A leap year has 366 days, but not every fourth year gets one: 1900 and 2100 are skipped because century years must also divide by 400, as 2000 did.

How many feet are in a mile, a unit the Romans defined by counting a marching soldier's paces?

A mile is 5,280 feet because Elizabethan England fixed it in 1593 at 8 furlongs of 660 feet each, rather than the Romans' 5,000 feet.

How many seconds are in a day, the product of 24 hours, 60 minutes and 60 seconds?

A day has 86,400 seconds, 24 × 60 × 60, except on the rare days a leap second is added to keep clocks in step with Earth's uneven spin, 27 times between 1972 and 2022.

How many five-cent nickels add up to one dollar, coins that are mostly copper despite their name?

20 nickels make a dollar, and the coin is 75% copper and only 25% nickel; when metal prices spiked in 2007 the metal in one was worth more than five cents.

How many pins stand in a bowling triangle of four rows, with one pin at the front and four at the back?

10 pins, 1 + 2 + 3 + 4, form a triangle, and knocking all of them down with the first ball is a strike, with the second ball a spare.

How many sides does a British 50p coin have, a shape picked in 1969 so it would still roll through vending machines?

The 50p has 7 sides, each curved so the coin's width is the same whichever way you measure it; it was the world's first seven-sided coin and prompted a group of 'Anti-Heptagonists'.

How many ounces are in a pound, the unit whose odd abbreviation lb comes from the Roman libra?

A pound is 16 ounces, and 'pound' itself comes from the Latin libra pondo, 'the weight measured in libra', the Roman unit that gave us the lb sign.

Which number is the smallest prime, and the only prime that is not odd?

2 is the only prime that is not odd, since any larger non-odd number is 2 times something smaller; 1 is left out of the primes by definition.

How many 0s follow the 1 when one billion, a thousand millions, is written out in digits?

A billion is 1 followed by 9 zeros, 1,000,000,000, in the short scale now standard in English; older British usage made a billion a million millions and called this number a milliard.

How many inches are in a foot, in the old English system where three feet make a yard?

A foot is 12 inches, and since the United States adopted the international inch on 1 July 1959 each inch has been exactly 2.54 cm, making a foot 30.48 cm.

How many cells does a standard Sudoku grid hold, nine rows of nine that are also split into nine 3×3 boxes?

A Sudoku grid has 81 cells, 9 × 9, and the modern puzzle was designed anonymously by a 74-year-old retired architect from Indiana and published in 1979 as 'Number Place'; Japan renamed it in 1986.

In the number 3,512, what is the digit 3 worth, sitting in the place furthest to the left?

The 3 is worth 3,000, because each place to the left multiplies a digit by another ten: 3 × 1,000, 5 × 100, 1 × 10 and 2 × 1 add up to 3,512.

How much fence goes all the way round a rectangular garden 9 m long and 4 m wide?

The fence is 26 m, twice 9 plus twice 4, which is the perimeter; the area, 9 × 4 = 36 square metres, is a different question, and 'perimeter' is Greek for 'measure around'.

What fraction of a pizza is left after three of its eight equal slices are eaten?

5/8 of the pizza is left, because 8/8 − 3/8 = 5/8 when the bottom numbers match, and that works out at 0.625, or 62.5%.

What fraction of an hour is 20 minutes, an hour being 60 minutes long?

20 minutes is 1/3 of an hour, since 20/60 simplifies to 1/3; the 60-minute hour comes down from medieval astronomers who followed Babylonian practice.

A film starts at 6:40 pm and runs for 95 minutes; at what time does it end?

It ends at 8:15 pm: 95 minutes is 1 hour 35 minutes, so 6:40 plus an hour is 7:40, and 35 more minutes reaches 8:15.

Which mark separates whole numbers from tenths in the United States and Britain, where much of Europe uses a comma?

A dot on the line, the full stop, became the English-speaking world's decimal mark after John Napier used it in his logarithm tables of 1614 and 1619.

How many grams are in a kilogram, a unit first defined in 1795 as the mass of one litre of water?

A kilogram is 1,000 grams, and since 2019 it has been defined through the Planck constant instead of the platinum-iridium cylinder that served as the standard for 130 years.