A building has ground floor and 10 more floors. Nine persons enter in a lift at the ground floor. The lift goes up to the 10th floor. The number of ways, in which any 4 persons exit at a floor and the remaining 5 persons exit at a different floor, if the lift does not stop at the first and the second floors, is equal to :
- 2184
- 3064
- 7056
- 11340
Answer
(3) 7056
Solution
The lift does not stop at floors 1 and 2, so persons can exit only at floors 3 to 10, i.e. at 8 floors.
Select the 4 persons who exit together: 9C4=126 ways (the remaining 5 form the other group)
Floor for the group of 4: 8 ways
A different floor for the group of 5: 7 ways
Number of ways =126 8 7=7056
Answer: (3)