Deepthi Subbu wrote:Liam is pulled for over speeding just as he is arriving to work. He explains to the police officer that he cannot afford to be late today , and has arrived at work only 4 minutes before he is to start.The officer explains that if Liam had driven 5mph slower for his whole commute , he would have arrived at work exactly on time . If Liam's commute is 30 miles long , how fast was he actually driving? (Assume that Liam drove at a constant speed for the duration of his commute)
I partly understand the problem but am not sure of the role played by the data 4 mins and the method to solve .
OA 50
The problem states that Liam arrived 4 minutes early and that, if he had traveled 5mph slower, the trip would have taken 4 more minutes, enabling him to arrive on time.
Since the GMAT would provide us with answer choices, we could plug them in for Liam's actual speed.
Answer choice: actual speed = 50mph
Time at 50mph = d/r = 30/50 = 3/5 hour.
Time at 45mph (5mph slower) = d/r = 30/45 = 2/3 hour.
Difference in time = 2/3 - 3/5 = 1/15 hour = 4 minutes. Success!
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