The answer is exactly 50%, "regardless" of the underlying population – the probability of picking 3 and then 7 is the same as picking 7 and then 3, regardless of the particular probability of picking 3 or 7. Thus, if one picks a single sample point "X"1, then 50% of the time the next sample point will be greater, which yields ("X"1, +∞) as a 50% prediction interval for "X"2. Similarly, 50% of the time it will be smaller, which yields another 50% prediction interval for "X"2, namely (−∞, "X"1). Note that the assumption of a continuous distribution avoids the possibility that values might be exactly equal; this would complicate matters.