Probability Puzzle: What are the chances that "Subject A" will call "Subject B"?

1. Neither Subject A nor Subject B knows that a study is being performed
2. Subject A can only place one call to Subject B during a specific span of 99 consecutive days and nights (one ring only)
3. Subject B can only sit at his desk during the same span of 99 consecutive days and nights (one second only)
4. Both parties have 24 hour access to place a call or sit at desk
5. Both parties operate on a random schedule, where one moment is not favored over another (during a 24-hour period)
6. Subject A lives 12,000 miles from Subject B

BigJohn said:

Dear Friends:

I recently approached a university math professor with this puzzle, but she could not answer it or couldn't find the time. So, here goes nothing: What are the chances that "Subject A" will call "Subject B", the very second Subject B sits down at his desk?

Please be advised:

1. Neither Subject A nor Subject B knows that a study is being performed
2. Subject A can only place one call to Subject B during a specific span of 99 consecutive days and nights (one ring only)
3. Subject B can only sit at his desk during the same span of 99 consecutive days and nights (one second only)
4. Both parties have 24 hour access to place a call or sit at desk
5. Both parties operate on a random schedule, where one moment is not favored over another (during a 24-hour period)
6. Subject A lives 12,000 miles from Subject B

So, what are the chances that Subject A calls Subject B at precisely the same moment that Subject B comes to rest in his chair?

Thanking you in advance - Big John

P.S. If you are able to figure this out, please share with me how you went about solving it. Thank you.

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