How is standard cost computed when there are co-products and by-products?

(1) Add all the costs of the materials + overhead - product
(2) Whatever is left, split by percentage set in cost apportionment of the main product found in the material master

Example of the computation: 

Let's assume the following for the apportionment: 

Main Product - 670

Co-Product 1 - 322

Co-Product 2 - 8