Probability of seven positive and three negative = c (= c (=C( 10/0,3) * 0.510.
Probability of five positive and five negative = c (= c (=C( 10/0,5) * 0.510.
Let these three events be expected events, and the probability of events = [c (10,3)+c (10,3)+c (10,3)] * 0.510 = 0.48.
This probably constructs an event with a probability of 0.48.
This is an idea. In an experiment, probability is constructed according to different probabilities of different results. It can also be constructed by taking the probability of different events, and the time of different tests can be different.
Theoretically, it is possible to construct an event with an arbitrary probability of p, but the difficulty lies in the fact that in the process of construction, it is necessary to continuously bring in data for calculation, and then deduce the required data according to the result error.