Option D, For a standard normal distribution, the expression that is always equal to 1 is P(z ≤ -a) + P(-a≤z≤a) + P(Z≥a).
<h3>
What is standard normal distribution?</h3>
A standard normal distribution is a normal distribution with a mean of zero and standard deviation of 1.
For a standard normal distribution, the total area of a curve is always equal to 1.
total area = P(z≤-a)+P(-a≤z≤a)+P(Z≥a) = 1
Thus, for a standard normal distribution, the expression that is always equal to 1 is P(z ≤ -a) + P(-a≤z≤a) + P(Z≥a).
Learn more about standard normal distribution here: brainly.com/question/4079902
#SPJ1
