the elevator in an 11 - 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 4 - hour period ? Select:  A) 88  B) 56  C) 42  D) 34  E) 64

Rationale: complete trip = 10 floors up and 10 floors down = 20 floors = 20 * 1 / 4 = 5 minutes plus 2 minutes = 7 minutes . 4 hour = 240 minutes . in 240 minutes operator can make 240 / 7 = 34 trips . answer : d .
Answer: D