Aptitude - Simplification - Discussion
Discussion Forum : Simplification - General Questions (Q.No. 15)
15.
David gets on the elevator at the 11th floor of a building and rides up at the rate of 57 floors per minute. At the same time, Albert gets on an elevator at the 51st floor of the same building and rides down at the rate of 63 floors per minute. If they continue travelling at these rates, then at which floor will their paths cross ?
Answer: Option
Explanation:
Suppose their paths cross after x minutes.
Then, 11 + 57x = 51 - 63x 
120x = 40
| x = | 1 |
| 3 |
| Number of floors covered by David in (1/3) min. = |  |
1 | x 57 |  |
= 19. |
| 3 |
So, their paths cross at (11 +19) i.e., 30th floor.
Discussion:
28 comments Page 3 of 3.
Diwakar Ramachandra said:
6 years ago
Since, both X and Y are traveling in opposite directions, their relative speed = (57+63) floor/minute = 120f/m.
Total distance between X an Y in terms of floors = 51-11=40 floors.
Therefore, time taken to cross each other = Distance/Speed = 40/120= 1/3 minutes.
Distance (floors) traveled by X in 1/3 minutes = Speed x Time = 57 x 1/3 = 19 floors.
So, X would have travelled to 11 + 19 = 30 floors when the meet/cross each other.
Total distance between X an Y in terms of floors = 51-11=40 floors.
Therefore, time taken to cross each other = Distance/Speed = 40/120= 1/3 minutes.
Distance (floors) traveled by X in 1/3 minutes = Speed x Time = 57 x 1/3 = 19 floors.
So, X would have travelled to 11 + 19 = 30 floors when the meet/cross each other.
(9)
Akshatha said:
6 years ago
Can anyone tell me the problem meaning step by step?
(3)
Akshay said:
5 years ago
Taking the ratios 57:63
We get 19:21.
David is in 11th floor. David is going upward direction. So 11+19=30th floor.
Otherwise, Albert is in the 51st floor and he goes downward. So 51-21=30th floor.
We get 19:21.
David is in 11th floor. David is going upward direction. So 11+19=30th floor.
Otherwise, Albert is in the 51st floor and he goes downward. So 51-21=30th floor.
(27)
Monsahab said:
5 years ago
Anyone, explain the Solution, please.
(1)
Finara said:
5 years ago
David's starting position = 11th floor.
Albert's = 51st,
So, distance covered by david till the point they meet= x
and for Albert= (40-x)
Speed of David = 57 floors/minute
and for Albert = 63 floors/minute.
As time taken by both will be same equation becomes:
(x/57) = (40-x)/63
x = 19.
Thus, answer is (11+19) or (51-21) => 30th Floor.
Albert's = 51st,
So, distance covered by david till the point they meet= x
and for Albert= (40-x)
Speed of David = 57 floors/minute
and for Albert = 63 floors/minute.
As time taken by both will be same equation becomes:
(x/57) = (40-x)/63
x = 19.
Thus, answer is (11+19) or (51-21) => 30th Floor.
(5)
Anil Sah said:
5 years ago
Not understanding, Please anyone help me to get it.
Rasel Azam said:
3 years ago
First-person is now at the 11th floor while the second person now at the 51th floor.
First person is moving upward and the second person is moving downward staying in two different lift.
The question is at which floor their lift meets i.e they meet or they cross each other. Their lift speeds are 57 floor/ minute and 63 floor/minute respectively.
Solution:
Let, at the x floor they meet, such that 11<= x<=51.
Therefore, to reach the meeting floor first person will cover a distance of (x-11) floors
and the second person will cover a distance of (51-x) floor.
As their speeds are different but they start the journey at the same time, to reach the meeting floor they need equal time i,e t1=t2
Therefore, t1=t2.
>> (x-11)/57=(51-x)/63 [t=s/v formula].
>> x=30
Therefore, at 30th floor, their lift will cross each other or they will meet.
First person is moving upward and the second person is moving downward staying in two different lift.
The question is at which floor their lift meets i.e they meet or they cross each other. Their lift speeds are 57 floor/ minute and 63 floor/minute respectively.
Solution:
Let, at the x floor they meet, such that 11<= x<=51.
Therefore, to reach the meeting floor first person will cover a distance of (x-11) floors
and the second person will cover a distance of (51-x) floor.
As their speeds are different but they start the journey at the same time, to reach the meeting floor they need equal time i,e t1=t2
Therefore, t1=t2.
>> (x-11)/57=(51-x)/63 [t=s/v formula].
>> x=30
Therefore, at 30th floor, their lift will cross each other or they will meet.
(13)
DAg said:
2 years ago
Thanks for the answer @ Finara.
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