Number
Fractions
A fraction tells you into how many equal pieces you divide something and how many pieces you take. Different fractions can be the same piece.
Topics
All topics
Pick a topic. Each one starts with a question, shows a picture to play with, explains the rule and lets you practise.
16 topics
Number
Fractions, percentages, negative numbers, powers and the order of operations.
- Number
Adding and subtracting fractions
You add or subtract fractions when they have the same denominator. If they do not, you first give them a common denominator.
- Number
Percentages
One percent is one hundredth. With percentages you compare parts of different sizes and work out discounts and price rises.
- Number
Negative numbers
Negative numbers lie to the left of zero on the number line. You use them for temperatures below zero, debts and floors below ground.
- Number
Powers and square roots
A power is a short way to write the same number multiplied by itself many times. The square root goes back the other way: which number gave this square?
- Number
Order of operations
When several operations follow each other, we agree on a fixed order: brackets, powers, times and divide, plus and minus. That way everyone gets the same answer.
Algebra
Working with letters, equations, ratios and linear functions.
- Algebra
Algebraic expressions
A letter stands for a number you do not know yet or that can change. You calculate with it just like with numbers: collect like terms, expand brackets, substitute values.
- Algebra
Linear equations
An equation is a balance in equilibrium. Do the same to both sides and it stays balanced, until only x is left.
- Algebra
Ratios and proportion
A ratio compares two quantities. For directly proportional quantities the quotient stays the same, for inversely proportional ones the product does.
- Algebra
Linear functions
A linear function y=
ax+ b gives a straight line. b is where you start on the y-axis, a is how much y changes per step in x.
Geometry
Angles, perimeter and area, the circle and Pythagoras' theorem.
- Geometry
Angles
An angle tells you how far you turn. You measure it in degrees, give it a name and calculate with fixed sums such as 180° in a triangle.
- Geometry
Perimeter and area
The perimeter is the length of the edge around a shape, in metres. The area is how much space lies inside it, in square metres.
- Geometry
The circle
The circumference of every circle is a little more than three times its diameter: that number is called π. With it you work out the circumference and area of anything round.
- Geometry
Pythagoras' theorem
In a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides: a^2+
b^2= c^2.
Data and probability
Mean, median and mode, and how likely something is.
- Data and probability
Mean, median and mode
Three ways to say with a single number what is typical in a set of data: the mean, the middle value and the value that appears most often.
- Data and probability
Probability
A probability says how likely something is, as a number between 0 and 1: the number of favourable outcomes divided by the number of possible outcomes.