# Proportion

Understanding Proportion

• Proportion: Is a relationship showing how two or more amounts compare to each other. It can be expressed as two ratios or fractions that are equal to each other.

• Direct Proportion: This occurs when two quantities increase or decrease at the same rate. It can be expressed as y ∝ x (y is directly proportional to x) or y = kx (where k is the constant of proportionality).

Direct and Inverse Proportions

• Inverse Proportion: Conversely, this is a relationship where an increase in one quantity corresponds to a decrease in another. Expressed as y ∝ 1/x (y is inversely proportional to x) or y = k/x.

• Recognising proportionality: In cases of direct proportion, graphs through the origin will have a straight line, while inverse proportion graphs will have a hyperbolic curve.

Solving Proportional Problems

• Finding the constant of proportionality: To determine the constant (k), use known values of x and y and solve the equation.

• Solving for unknowns: When given a proportional equation and a set of values, substitution will help solve for unknowns.

• Unitary method: This technique involves first finding the value of a single unit, which can then be used to find the values of the multiples.

Applying Proportional Relationships

• Direct variations: This is when the ratio of two variables is constant. For instance, if speed is directly proportional to time, then doubling the time will also double the speed.

• Inverse variations: In this scenario, the product of the two variables is constant. As an example, if speed is inversely proportional to time, then doubling the time will halve the speed.

• Combining types of proportionality: A combination of direct and inverse proportionality can also occur, for example, y ∝ x/z (y is directly proportional to x and inversely proportional to z).