After knowing your allocated ratio of 50%
How do I get the total share of a partner who's beginning balance is 50.000

Please do not keep posting the same question over and over as it just causes confusion. I've deleted your duplicate posts.

If the allocation of income/loss is 50%, then 50% of the income/loss goes to the partner's account. This is not based on their beginning balance and has nothing to do with it. The balance of the account will obviously increase with a share of income, but it's not what determines the share to begin with.