How to derive a suitable formula for a probability distribution?

Question

Algebra

Hello!
I rewrote this question more briefly. I need to calculate the probability of an event occurring (first calculate the probability table with events, then use it to calculate which event has happened right now). The columns that I wrote are just tables of the distribution of the probability of the occurrence (occurrence) of an event. Example:
65% chance to roll 100%
15% chance to roll 80%
10% chance to roll 60%
5% chance to roll 55%
5% chance to roll 50%
i.e. . (B is the probability, D is the desired event)
B = 65%, D = 100%
B = 15%, D = 80%
B = 10%, D = 60%
B = 5%, D = 55%
B = 5% , D = 50%
A certain N affects the calculation of the table. In this case, I took N = 65%, and for the remaining 35%, the formula should describe how much D will fall out (I painted this at random above).
After that, calculate what probability I am currently in and get D corresponding to this probability. For example, I got into 10%, so I got D = 60%.
Actually, how to calculate the formula for calculating the occurrence of an event by probabilities?