The elevator in an eleven-story office building travels at

Question

The elevator in an eleven-story office building travels at the rate of one floor per 1/4 minute, which allows time for picking up and discharging passengers. At the main floor and at the top floor, the operator stops for 1 minute. How many complete trips will an operator make during a 7-hour period?

A) 88
B) 56
C) 42
D) 60
E) 64

A) 88
B) 56
C) 42
D) 60
E) 64

Bunuel · Accepted Answer

The elevator in an eleven-story office building travels at the rate of one floor per 1/4 minute, which allows time for picking up and discharging passengers. At the main floor and at the top floor, the operator stops for 1 minute. How many complete trips will an operator make during a 7-hour period?

A) 88
B) 56
C) 42
D) 60
E) 64

A) 88
B) 56
C) 42
D) 60
E) 64

Complete trip = 10 floors up and 10 floors down = 20 floors = 20*1/4 = 5 minutes plus 2 minutes = 7 minutes.

7 hour = 420 minutes.

In 420 minutes operator can make 420/7=60 trips.

Answer: D.

Hope it's clear.

Bunuel · Answer

Think below might help:

(1st floor = 1 minute) 
(1/4 minutes to 2nd floor) 1
(1/4 minutes to 3rd floor) 2
(1/4 minutes to 4th floor) 3
(1/4 minutes to 5th floor) 4
(1/4 minutes to 6th floor) 5
(1/4 minutes to 7th floor) 6
(1/4 minutes to 8th floor) 7
(1/4 minutes to 9th floor) 8
(1/4 minutes to 10th floor) 9
(1/4 minutes to 11th floor) 10

(11th floor = 1 minute) 
(1/4 minutes to 10th floor) 1
(1/4 minutes to 9th floor) 2
(1/4 minutes to 8th floor) 3
(1/4 minutes to 7th floor) 4
(1/4 minutes to 6th floor) 5
(1/4 minutes to 5th floor) 6
(1/4 minutes to 4th floor) 7
(1/4 minutes to 3rd floor) 8
(1/4 minutes to 2nd floor) 9
(1/4 minutes to 1st floor) 10

Complete trip = 20 1/4-minute intervals + 2 minutes = 7 minutes.

Does this make sense?

vishal4584 · Answer

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.

Berbatov · Answer

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

JusTLucK04 · Answer

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

JusTLucK04 · Answer

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

JeffTargetTestPrep · Answer

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

Fdambro294 · Answer

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

kpop1234567890 · Answer

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

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

ic2022 · Answer

Hi, Why are you not considering Ground floor as well, so it makes 22*1/4 + 2 minutes for a single trip - making the answer 56 mins for 7 hours. Any building with n floors will also have a ground floor making the total count for lift as n+1.

Bunuel · Answer

The question clearly states it’s an  eleven-story  building, which already includes the main (ground) floor as one of the stories.

So, going from the  1st to the 11th floor  involves  10 floor-to-floor movements , not 11. Likewise, coming back down is another 10. That's why the total is 20 movements, each taking 1/4 minute.

There’s no need to add an extra floor for the ground floor, it’s already counted as the 1st story. Please review the discussion above for more.

agrotechpepper · Answer

hi, pretty clear explaination. The mistake I was doing that adding another  1 min,  post finally coming to ground (main) floor for discharging. So I was calculating 1min (Main Floor Stop) + 2.5 min (Ascent) + 1 min (Top floor Stop) + 2.5 min (Descent) +1 min (Main floor Stop) = 8 mins. Any tips (any word I missed) where I went wrong? Help, so as to avoid being wrong in future.

The elevator in an eleven-story office building travels at

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

The elevator in an eleven-story office building travels at

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards