Three persons must exit at three different floors.
The lift goes to the 10th floor and does not stop at floors 1, 2, and 3.
Available floors for exit: 4, 5, 6, 7, 8, 9, 10 (7 floors total).
The number of ways to assign 3 persons to 3 different floors from 7 available floors is a permutation problem: P(7,3)=7×6×5=210.
Alternatively, choose 3 floors from 7 and arrange 3 persons: 7P3=35×6=210.