Math & Numbers Facts for Kids
Mind-bending number facts
Eratosthenes calculated the circumference of the Earth around 240 BC using maths alone β measuring shadows and angles β and came remarkably close to the correct answer of about 40,075 kilometres.
Multiplying two odd numbers always gives an odd result, and multiplying two even numbers always gives an even result. But multiplying any even number by any odd number always gives an even result.
Using letters such as x and y to represent unknown numbers in algebra was popularised by French mathematician François Viète in the 1590s. Before this, all algebra problems were written out in words.
The number seven is considered lucky in many cultures around the world. Mathematically it is special too β it is the largest prime number you need to check when determining if a two-digit number is prime.
Exponent notation is a shorthand for repeated multiplication: 2β΅ means 2 Γ 2 Γ 2 Γ 2 Γ 2 = 32. This notation was first used by RenΓ© Descartes in his 1637 book 'La GΓ©omΓ©trie'.
Web designers use hexadecimal (base-16) colour codes to specify colours. The code #FF0000 means maximum red, no green, and no blue, giving a pure red β the 'FF' equals 255 in decimal.
The number 1,729 is known as the HardyβRamanujan number. The mathematician Ramanujan noticed it is the smallest number expressible as the sum of two cubes in two different ways: 1Β³ + 12Β³ and 9Β³ + 10Β³.
A quick way to check if a number is divisible by 9 is to add up its digits: if the total is divisible by 9, so is the original number. For example, 729: 7 + 2 + 9 = 18, and 18 Γ· 9 = 2, so 729 is divisible by 9.
Mathematicians describe movements of shapes using three basic transformations: reflection (flipping), rotation (turning), and translation (sliding). A fourth transformation, enlargement, changes the size of the shape.
In the Monty Hall problem, a game show contestant chooses one of three doors β one hides a prize. After the host opens a losing door, switching to the other door gives a 2/3 chance of winning, better than staying at 1/3. Most people find this result very surprising.