Given odds against of an event say A is given to be 7 : 2 , therefore probability of happening of the event A i.e. P(A) = 2/(7+2) = 2/9 & probability of not happening of the event A that is P(A') = 7/9 .

p. 491) In other words, the D in D-Day merely stands for Day. This coded designation was used for the day of any important invasion or military operation.

Many experts have varying opinions, including that the D simply stood for "day," a code used for any important military operation. Others have said it's just alliteration, like "H-Hour," when a military assault begins.