Well the complete business consists of both the parts and the fridge division right? and parts division is 1/2 the size of fridge division?
So if you look at it, the complete organization is:
33% Parts
66% Fridge
When pro rata is applied, 2/3 or 66% (Fridge business) is applied on the TOTAL amounts of the organization, leaving out the 1/3 or 33% (Parts business).
The parts business still is 1/2 or 50% of the fridge business. I.e. 33/66 = 50%