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Emil-Kunkin March 9, 2022
Hi Ben,The passage tells us that everyone sitting had registered for a clinic that no accomplished tennis player would take. We are told that three people were in the room. This does not eliminate the possibility of a fourth, fifth, or even more people also sitting in the room.
By analogy, we could say that Washington and Lincoln are on mount rushmore, and everyone on mount rushmore was a president. That does not mean that George andAbe are the only two people on Mount rushmore. All we know from this example is that anyone else on mount rushmore (like Jefferson) was also a president.
Back to the question- there could have been additional people sitting in the room- but if there were, we know that they were also registered for the clinic.