Over a large number of trials, the probability of an event _____is equal to the probability that it will not occur.
a. occurring b.to occur
Which one is right, and why? Pls.
That example sentence is taken from an exam question (Source), the answer to which is occurring:
23. Over a very large number of trials, the probability of an event's occurring is equal to the probability that it will not occur.
The same form, possessive noun + gerund, is found here in a dictionary entry (Source):
a. The ratio of the probability of an event's occurring to the probability of its not occurring.
Note, however, that the noun event doesn't have to take apostrophe s. Here are two example (of many) from Google search:
Negation Rule: The probability of an event occurring is equal to 1 minus the probability of it not occurring.
The probability of an event occurring is equal to the ratio of desired outcomes to the total number of possible outcomes
The reason that some writers add 's and some don't has to do with where the word occurring sits in the sentence. It functions as a nominal modifier, and gerunds and adjectives (i.e., present participles) fit that slot nicely.
Gerund: event's occurring
Participle: event occurring <reduced from that will occur>
Is there a difference in meaning? What say our members?