Year 8 vocabulary glossary

ratio

A ratio compares two or more quantities, showing how much of one there is compared to another, such as 2:3.

simplify a ratio

To simplify a ratio means to divide all parts by their highest common factor, writing it in its simplest form.

share in a ratio

Sharing in a ratio means splitting a total amount into parts that match a given ratio.

unitary method

The unitary method solves ratio and proportion problems by first finding the value of one unit or one share.

percentage

A percentage is a fraction out of 100, shown using the % symbol, such as 45%.

percentage increase

A percentage increase is a rise in an amount, calculated as a percentage of the original value.

percentage decrease

A percentage decrease is a fall in an amount, calculated as a percentage of the original value.

original amount

The original amount is the starting value before any percentage increase or decrease is applied.

compound interest

Compound interest is interest calculated on both the original amount and any interest already added, so it grows each year.

simple interest

Simple interest is interest calculated only on the original amount, staying the same each year.

depreciation

Depreciation is a decrease in the value of something, such as a car, over time, often given as a percentage per year.

principal

The principal is the original sum of money invested or borrowed, before any interest is added.

multiplier

A multiplier is a single decimal number used to increase or decrease an amount by a percentage in one calculation, such as 1.2 for a 20% increase.

significant figure

A significant figure is a digit that carries meaning in a number, counted from the first non-zero digit.

decimal place

A decimal place is a digit's position after the decimal point, used when rounding decimals.

round to significant figures

Rounding to significant figures means giving an approximate value using a set number of meaningful digits, such as 3 significant figures.

per cent

Per cent means 'out of 100' and is the idea behind every percentage.

reverse percentage

A reverse percentage problem works backwards from a value after a percentage change to find the original amount.

best buy

A best buy comparison uses unit price to work out which of two or more products offers better value for money.

unit price

The unit price is the cost of a single unit of an item, such as price per 100g, used to compare value.

part:part ratio

A part:part ratio compares two parts of a whole directly to each other, such as boys:girls.

part:whole ratio

A part:whole ratio compares one part to the total amount, often written as a fraction.

expand

To expand means to multiply out brackets in an expression, removing the brackets by multiplying each term inside by what is outside.

single bracket

A single bracket expression, such as 3(x + 2), has one term multiplying everything inside one pair of brackets.

expand and simplify

To expand and simplify means to multiply out brackets and then collect any like terms into a shorter expression.

collect like terms

Collecting like terms means combining terms with the same letter part into a single term, such as 3x + 2x becoming 5x.

linear equation

A linear equation is an equation where the unknown appears only to the power of 1, with no squared or higher terms.

two-step equation

A two-step equation needs two operations to solve for the unknown, such as 2x + 3 = 11.

gradient

The gradient of a line measures its steepness, calculated as the change in y divided by the change in x.

y-intercept

The y-intercept is the point where a graph crosses the y-axis, where x = 0.

x-intercept

The x-intercept is the point where a graph crosses the x-axis, where y = 0.

straight-line graph

A straight-line graph shows a linear relationship between two variables, forming a straight line when plotted.

y = mx + c

y = mx + c is the standard form of a linear equation, where m is the gradient and c is the y-intercept.

table of values

A table of values lists pairs of x and y values, calculated from an equation, ready to be plotted as points on a graph.

axis (axes)

An axis is one of the reference lines on a graph, usually the horizontal x-axis and vertical y-axis; axes is the plural.

origin

The origin is the point (0, 0), where the x-axis and y-axis meet on a graph.

coordinate

A coordinate is a pair of numbers, (x, y), that gives the exact position of a point on a graph.

plot (a graph)

To plot a graph means to mark coordinate points accurately and, if appropriate, join them to show a relationship.

transformation

A transformation changes the position, size or orientation of a shape, such as by translating, reflecting or rotating it.

translation

A translation moves every point of a shape the same distance in the same direction, without turning or resizing it.

reflection

A reflection flips a shape over a mirror line to create a mirror image.

mirror line

A mirror line is the line a shape is reflected across, with each point mapped to an equal distance on the other side.

rotation

A rotation turns a shape a given angle around a fixed point, called the centre of rotation.

centre of rotation

The centre of rotation is the fixed point a shape turns around during a rotation.

volume

Volume is the amount of 3-D space a shape occupies, measured in cubic units such as cm³.

cuboid

A cuboid is a 3-D shape with six rectangular faces, like a box.

prism

A prism is a 3-D shape with two identical, parallel end faces (the cross-section) connected by flat rectangular faces.

cross-section

The cross-section is the flat shape you get by slicing straight through a 3-D shape, especially the repeated end-shape of a prism.

surface area

Surface area is the total area of all the faces of a 3-D shape added together.

face

A face is one of the flat surfaces that make up a 3-D shape.

edge

An edge is a line where two faces of a 3-D shape meet.

parallel lines

Parallel lines are straight lines that stay the same distance apart and never meet, no matter how far they extend.

transversal

A transversal is a straight line that crosses two or more other lines, often two parallel lines.

corresponding angles

Corresponding angles are equal angles found in matching positions where a transversal crosses parallel lines.

alternate angles

Alternate angles are equal angles found on opposite sides of a transversal, between two parallel lines, forming a Z shape.

co-interior angles

Co-interior angles lie between two parallel lines on the same side of a transversal and always add up to 180 degrees.

pie chart

A pie chart is a circular chart divided into sectors, where each sector's angle shows its proportion of the whole data set.

sector

A sector is a 'slice' of a circle, bounded by two radii and an arc, used in pie charts.

scatter graph

A scatter graph plots pairs of values as points, used to show whether there is a relationship between two variables.

correlation

Correlation describes the relationship between two variables on a scatter graph, such as whether they increase together.

positive correlation

Positive correlation means that as one variable increases, the other variable tends to increase too.

negative correlation

Negative correlation means that as one variable increases, the other variable tends to decrease.

no correlation

No correlation means there is no clear relationship between the two variables on a scatter graph.

line of best fit

A line of best fit is a straight line drawn through a scatter graph, as close as possible to all the points, showing the trend.

bivariate data

Bivariate data is data made up of pairs of related values for two variables, such as height and shoe size.

interpolate

To interpolate means to estimate a value that lies between two known data points on a graph.

extrapolate

To extrapolate means to estimate a value beyond the range of the data already collected, which carries more risk of being wrong.