Z-score concept is a Numerical measurement which describes the value's relationship to the mean group of values . Z-score is always measure in terms of standard deviation from the mean.
we have now the value of z at hand, we need to check the standard normal table to determine the probability of this value that will be
The proportion of the population that have a protein requirement less than 0.60 g P • kg-1 • d-1 is 0.239, that is, 239 persons for every 1000, or simply 23.9% of them.
With this value for z at hand, we need to consult a standard normal table to determine what the probability of this value is.