In the foundations section in Phil Galfonds “This Is PLO” course, he goes through how often you are dealt a random 2 card combo in PLO.
On a 987 flop, he says that there is approximately 7% of having a 2 card combo not connected with the flop. So 7% of having each of TJ, T6 & 56 giving you a straight. Combining the probability of all these combos (seeing that they overlap) gives a probability of 19.6% according to Phil.
Question is: How do you calculate the frequency of how often you have a straight on 987 board?