GMAT Challenge Series (700+): Q10

Waiting for Elevator.jpg


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

MBA Wisdom's Answer:

$$\text{A complete trip comprises of:}$$ $$\text{Stop at first floor: 1 min}$$ $$\text{10 floors up: 2.5 min}$$ $$\text{Stop at top floor: 1 min}$$ $$\text{10 floors down: 2.5 min}$$ $$\text{Total trip time: 7 min}$$ $$$$ $$\text{7 hours} = {{7} \times {60}} \text{ min} = {420} \text{ min}$$ $${trips} = {\text{time} \over \text{trip time}}$$ $${trips} = \frac{420}{7} = {60}$$

D. 60