Description of the numeracy involved:
When we see the word ‘ratio’, most of us think of formally written ratios such as the pupil : tutor ratio is 18 : 1, meaning that there are 18 students for every 1 tutor. In fact there are many calculations that can be thought of as ratios, and (believe it or not!), they are easier to understand if we do think of them in this way.
For example, if we think of the percentage 35% as 35 for every 100 then we can work out 35% of 50 kg by thinking proportionally:
35 for every 100 kg is the same rate/ratio as 17.5 for every 50 kg. So 35% of 50 kg is 17.5 kg.
This thinking makes the problem much easier to calculate than trying to work out 0.35 x 50 using the standard ‘percentage formula’, especially if the steps in the calculation have no meaning for the learner in terms of the quantities involved.