students should be given the opportunity (i.e. time) to debate
with the teacher remaining silent or encouraging other views to be aired, "I wonder if that is right?"
at some stage techniques will need to be considered though...
reversing the question could include:
can you devise proportions where
the concentrations are the same?
where A is slightly more concentrated than B?
where A is twice as concentrated as B?
I particularly like the account of strategies adopted by two 11 to 12 year old students, Karen and Alice, written about by Parmjit Singh
Karen is more confidently (flexibly) able to unitise and then compose these, iteratively, to a result