"Do you have a large sum?"
Translation:Tu ai o sumă mare?
I think you are asking why isn't it 'suma marea,' where 'suma marea' in your question means 'the largest sum'?
Sumă = sum Suma = the sum
But mare has a couple meanings, 'large' if you are using it as an adjective or it could also mean 'sea' if you use it as a noun. However when you say marea you are actually saying 'the sea'