Question

19. A lift in an office block has stopped at a restaurant on one of the floors. Call this floor zero. What floors does it stop at on the following sequence of journeys? Write each answer as either a positive or negative number. a) Up 8 floors b) then down 17 floors c) then down 12 floors d) then up 20 floors. ​

Answer 1

Answer:

An office block has five floors (ground, 1, 2, 3 and 4), all connected by a lift. When it goes up to any floor (except 4), the probability that after it has stopped it will continue to rise is 3/4. When it goes down to any floor (except the ground floor), the probability that after it has stopped it will continue to go down is 1/4. The lift stops at any floor it passes.

The lift is currently at the first floor having just descended. Calculate the probability of the following events:

a) its second stop is the third floor

b) its third stop is the fourth floor

c) its fourth stop is the first floor.

For part (a), I did this: P(first stop is the second floor)*P(second stop is the third floor) = (3/4)(3/4) = 9/16