A proportion can be written as a formula. The formula will consist of two variables and a constant. The constant `k` is the multiplier to one of the variables:
`y = kx`
Write a conversion for a currency conversion from Euros to British Pounds. The conversion rate is 1.2 Euros for every British Pound.
Check that the conversion is correct: for £1, you would expect more Euros.
Answer: `p = 1.2e`
A formula is shown as `x = 0.25y`. Rewrite this direct proportion to make `y` the subject.
Multiply both sides of the proportion by 4.
Answer: `4x = y`