A factory uses 2 machines to fill cartons with washing powder.
The cartons are labelled 'minimum contents 1.5kg'.
The mean mass delivered per carton by each machine is 1.515kg.
The median for machine A is 1.510kg, for machine B is 1.520kg.
Checks show that some cartons contain less than 1.5kg.
Which machine is likely to have filled them? Explain you reasoning.