How can children's concepts of partitioning need to be refined to produce a concept of fractional parts?

Answer 1

Dividing up pizzas works.
(cut it into 8 parts or 6 parts or whatever)

So does dividing up money, especially based on a dollar.
(use ten dimes or four quarters or twenty nickles or one hundred pennies...)

Answer 2

why is it obvious that 3/4 x 8/5 = 6/5?