Hi 

Please send the solution

Asked by Bovanghai | 4th May, 2019, 05:19: PM

Expert Answer:

Let us assume that their elevator cross each other after x minutes.
 
then, 11 + 57x = 51 - 63x
→ 120x = 40
→ x = 1/3
Number of floors covered by David in 1/3 mins = 1/3× 57 = 19
 
Therefore their elevator cross each other at 11 + 19 = 30th floor

Answered by Yasmeen Khan | 5th May, 2019, 04:13: PM