Number & Arithmetic

These articles cover the whole-number ideas everything else rests on. How a digit's place sets its value, the agreed order for working out a calculation, how numbers break into factors and primes, and how negative numbers behave when you add, subtract, multiply and divide them.

What Is Place Value? Digits, Base Ten and Expanded Form
Place value is the worth a digit has because of its position in a number. Each place is worth ten times the place to its right.
Order of Operations (BIDMAS and PEMDAS) Explained
The order of operations is the agreed sequence for working out a calculation: brackets, then powers, then multiplication and division, then addition and subtraction.
Factors and Multiples: What Is the Difference?
A factor of a number divides it exactly, with no remainder. A multiple of a number is that number times a whole number. So $4$ is a factor of $12$ , and $12$ is a multiple of $4$ .
Prime Numbers and Prime Factorisation with Factor Trees
A prime number has exactly two factors, $1$ and itself. Prime factorisation writes a number as a product of primes, such as $360 = 2^3 \times 3^2 \times 5$ .
Greatest Common Factor and Least Common Multiple (GCF and LCM)
The greatest common factor (GCF, or HCF) of two numbers is the largest number that divides both. The least common multiple (LCM) is the smallest number that both divide into.
Negative Numbers: Adding, Subtracting, Multiplying and Dividing
Negative numbers are numbers less than zero, written with a minus sign and placed to the left of zero on the number line. Together with zero and the positive whole numbers they form the integers.
Absolute Value: Distance from Zero, Equations and Inequalities
The absolute value of a number, written $|x|$ , is its distance from zero on the number line. Distances are never negative, so $|-4| = |4| = 4$ .