>>> A building has 10 floors. At the ground floor, 7 people enter the elevator. At the second floor, 3 people get off and 2 people enter. At the fourth floor, 5 people get off and 2 people enter. At the seventh floor, 1 person gets off and 3 people enter. Finally, at the tenth floor, everyone remaining in the elevator gets off. The question is, How many people were in the elevator when it started its journey, and how many total people exited the elevator by the end of its journey?

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At the end of the journey, only the 7 people who entered on the ground floor remained in the elevator.

During the journey, 11 people exited the elevator (7 on the ground floor minus 4 on the second floor, plus 3 on the seventh floor).

So, 18 people were in the elevator when it started its journey (7 people who entered on the ground floor plus 11 people who exited the elevator).