Algebraic Proportion

Algebraic Proportion

GCSE(F), GCSE(H),

A proportion can be written as a formula. The formula will consist of two variables and a constant. The constant is the multiplier to one of the variables:

y = kx

The conversion for miles to kilometres is:

5 miles converts to eight kilometres

and to calculate a conversion:

1 mile = frac(5)(8) or m = frac(5)(8)k

where m are miles and k are kilometres.

Examples

1. Write a conversion for a currency conversion from Euros to British Pounds. The conversion rate is 0.8 Euros for every British Pound.

Answer: p = 0.8e

Check that the conversion is correct: for 10 Euros, fewer Pounds are expected. 10 x 0.8 = £8.

2. A formula is shown as x = 0.25y. Rewrite this direct proportion to make y the subject.

Answer: 4x = y

Multiply both sides of the proportion by 4.