In this paper we discuss CP violations in and systems in the framework of the standard model. To start with, using only the experimental values of the moduli of the elements in the first two rows of the CKM matrix and its unitarity, we sought to fix the values of the complex phase angle , where . We find, in the PDG representation, that or . Next, we utilize the empirical information on the CP violation parameter in neutral kaon decays, the mixing parameter , the ratio and the theoretical results from the box diagrams for and in order to evaluate the range of values for the angle . The result is , which includes both and obtained earlier. This analysis also allows us to obtain the possible values of for a given angle , where is defined by . Thus, we are able to predict the possible values of the CP asymmetry parameter a in the neutral B-meson decays to CP self-conjugate states. Our results will be useful as the parameter a is expected to be measured in the near future.