If I buy a dress at 30% off the original price and I pay £40. How much was the dress originally?

I like to address this question by using similar fractions. That is to say x/y=2x/2y X over y is the same as 2x over 2y In this example we are asked what the full price of the dress is, as in what 100% of the price is. If the price paid is £40, which is a 30% reduction then the dress was bought at 70% of the original price. If X is the full price of the dress, which is the unknown value here, then (£)40/70(%) is the same as (£)X/100(%) 40/70 = X/100 40/70 multiplied by 100 = X X=£57.14 To check that we have solved the question correctly, find out 70% of £57.14 which is £39.99. Rounded up and the discounted price is £40 as outlined primarily in the question.