Question

answer this question with solution

Answer 1

Distance between them = 51= 11 = 40 floors 
relative speed = 57+63 = 120 floors/minute or 120 floors in 60 seconds. 

meaning the it will take 20 seconds for them to meet. In 20 seconds the lift with 63 floors /minute would have covered 63/3 = 21 floors. So the lifts will meet at 51-21 = 30th floor. 

30 is the answer.