Yves S. answered 05/11/20
Probability | Foundations of Statistics, Bayes & Combinatorics
Mark, what you calculated (or approximated) is the probability.
The odds is the ratio of p/q, with q=1-p
You are close!! Given the large numbers, your approximation for p is acceptable:
p < 420 / (8,400,000 - 27,500)