Why do this problem?
gives practice in working with volume in a context which anyone who bakes will recognise - when your recipe specifies a piece of equipment you don't have. Rather than just going out and buying another tin, you therefore want to see if what you have will do.
The depth of the 23cm round tin is deliberately omitted, since depth is rarely specified in a recipe in fact. Students will need to consider what depth such a tin might realistically have, and then see if they think the volume of cake mix will fit in it.
What is a realistic depth for the 23cm round tin?
What is the least depth the 23cm round tin could have, and still be suitable to bake the cake?
Once students have explored the question asked, they could then consider whether a round tin or a square one takes a bigger volume of cake mix for a given diameter. What's the equivalent of diameter in a square tin, is it the side length or the diagonal?
, which is a Stage 2 problem, would be a good warm-up problem.