Pseudo-random numbers are not random because they are predictable; given some initial sequence of PRNs, the future sequence can be determined.

True random numbers, on the other hand, are not predictable; regardless of the length of some initial sequence of TRNs, the future sequence can not be determined.

So, what percentage mix of TRN and PRN yields a sequence that is not predictable?

Another way to ask this question is, How perturb-able is the predictability of a PRNG?