The elevator in an eleven-story office building travels at

The answer is 60 (option D)
1----2-----3----4----5----6----7----8----9----10----11
0 1.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25

So the liftman will take 3.5 min for one way, so for complete trip, he will take 7 min.
(1.25 at the start is the lift rate + ome minute wait).

So, In 60 min,
The liftman will complete (60/7) trips.

therefore, in 7 hours, the number of complete trips will be (60/7)*7 ie 60 trips.

Ground floor (Main): 1 minute
Floor 1 - 10..........: 0.25 each * 10 floors = 2.5 mins per direction * 2 = 5 mins per round
Floor 11 (Top).......: 1 minute
=======================
..........................: 7 minutes per ride

7 * 60 mins = 420 mins in total

420/7 = 60

Even though it's a bit weird because in the first round, nobody has to leave and in the last round nobody enters

Thanks Gmatclub..I got more knowledge here for related to elevators.
Yes ....And I am agree with you that it will do 60 trip in 7 hours.
I want to say something about my services. We are also providing Home elevators and office elevators.

60*2= Main + 11 Floor
15*9= 135 Sec for 9 Floors

Total= 9+2 = 11 floors

Wat am I missing here..Coz 390 secs per trip does not lead to 60 trips in 7 hrs

So you included the 15 seconds for the ground floor/top floor too...for 1complete up-down trip?..I am counting it for just 9 floors

Got it..my interpretation was wrong

We are given that an elevator takes 1/4 minute to travel between floors and that it stops for one minute at the top floor and also on the main floor. Since the elevator is traveling from the main floor to the 11th floor, it’s traveling 10 total floors.

Thus, the total time it takes for the elevator to go from the bottom floor to the 11th floor and back down is:

20 x 1/4 = 5 minutes

Since the elevator stops for a minute each at the top and main floors, the amount of time to complete a trip is:

5 + 2 = 7 minutes = 7/60 hours

Thus, in 7 hours the elevator can complete 7/(7/60) = 60 trips.

Answer: D

The tricky part with the Elevator problems is realizing that if the building has 11 Stories, the elevator already starts out on the 1st Floor. The elevator does not do any traveling to get to the 1st Floor.

Then when it travels to the 2nd Floor, it has traveled 1 Story

when it travels to the 3rd Floor, it has traveled 2 Stories

....

when it travels to the 11th Floor, it has traveled 10 stories.


1 Complete Trip = Elevator going to the TOP, and then Elevator coming back DOWN

10 Stories traveled UP + 10 Stories traveled DOWN = 20 Stories traveled for a Complete Trip.

At the rate of 1/4th of a minute per Stories, the TIME spent traveling in a Complete Trip is:

20 Stories traveled * 1/4 min. per Story = 5 Minutes per 1 Complete Trip.


However, the elevator is also open for 1 minute on the 1st Floor and 1 minute on the Top Floor.
For Each Complete Trip, need to Add On +2 minutes for the stopping.

Total of 7 minutes per 1 Complete Trip.

7 hours = 420 minutes


How many Complete Trips can we make in 420 minutes when it takes 7 minutes per 1 Complete Trip?

420 / 7 = 60 Complete Trips

Answer D

I dont know in problems like this cultural context can play a part. In india we start with ground floor - so it means that you have to infact travel to get to even the first floor and you dont directly start at the first floor

Also the Q doesnt specify that it stops for 1 minute each at top and bottom floors