550 ml is the original amount in addition to the 18% that was given free We can write this as 550 = 100% + 18% = 118% 550 = 118% The first step to working this out is to work out what 1% of the drink is equivalent to To get from 118% to 1%, we must divide by 118 We do exactly the same to the drink 550/118 = 4.661ml We also know that 18% was given free 4.661 x 18 = 83.898ml Free 83.9ml free
