Because P(x = c) is zero for a continuous variable, P(c < x < d) and P(c <= x <= d) are:

1. Endpoints contribute no area under a density curve. 2. The probability that x takes on any single individual value is zero. 3. Adding the two endpoints therefore adds zero probability. 4. P(c < x < d) is the area to the right of c and left of d. 5. So the strict and non-strict interval probabilities are equal to each other. _Source: OpenStax Introductory Statistics 2e (CC BY 4.0), Ch 5 'Continuous Random Variables', sections 5.1-5.3_