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.
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.