Setting a maths enquiry/investigation for KS1?

I'm currently training to be a teacher and for one of my activities I have to set a maths enquiry/investigation. I have bought the things for a picnic for children to set out a table and set out a variety of food to share between them. They would have to scaffold their own knowledge of fractions etc and see if there's a different way of laying the table than they have.

I'm starting to think however that this may be a problem rather than an investigation as I was always led to believe that an investigation could have no answer. Or is it still an investigation as I haven't told them what outcome they could produce!?

Confused.

Can anyone help me turn this in to a solid investigation rather than a problem solving activity?