A portfolio can be divided between the two assets.
Define wi as the weight placed on asset i
With full investment, Swi = 1, where i = 1 to N (total number of assets)
If we fully invested in bonds, w1 = 1.00, w2 = 0.00
If we fully invested in stocks, w1 = 0.00, w2 = 1.00
This is asset allocation problem, where the investor has to decide how much to allocate across asset classes.