Myra drove at an average speed of 30 miles per hour for the first 30 miles of a trip, at an average speed of 60 miles per hour for the next 30 miles and at a average speed of 90 miles/hr for the remaining 30 miles of the trip. If she made no stops during the trip, Myra’s average speed in miles/hr for the entire trip was closest to
Choose the correct choice from the following choices:  A) The average speed is 35 miles per hour.  B) The average speed is 40 miles per hour.  C) The average speed is 45 miles per hour.  D) The average speed is 50 miles per hour.  E) The average speed is 55 miles per hour.
Here, Myra traveled at three speeds for one-third distance each.   Average Speed = 3abc/(ab + bc + ca) = 3*30*60*90/(30*60 + 60*90 + 30*90)   Average Speed = 3*2*90/(2 + 6 + 3) = 540/11   Answer (The average speed is 50 miles per hour.)
<result>D</result>
Myra drove at an average speed of 30 miles per hour for the first 30 miles of a trip, at an average speed of 60 miles per hour for the next 30 miles and at a average speed of 90 miles/hr for the remaining 30 miles of the trip. If she made no stops during the trip, Myra’s average speed in miles/hr for the entire trip was closest to