z-score is a statistical tool that is used to estimate the probability of finding a number in a normal distribution of data. Normal distribution is described as a function in which the mean is zero, the standard deviation is 1 and that the area under the curve is equal to 1. In this case, z =-1.96 is located at the left side of the graph and z = 1.96 is located on the other side. z =-1.90 is located between the mean and z = -1.96. This means finding the value with z = -1.90 is within the critical boundaries set by the test because the area inclusive covers z = -1.90.
