Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?
Options:
A) The average speed is 1/5 miles per hour.
B) The average speed is 1/3 miles per hour.
C) The average speed is 2/5 miles per hour.
D) The average speed is 2/3 miles per hour.
E) The average speed is 3/5 miles per hour.
We know the average speed and must find the fraction of time taken at a particular speed.   t1/t2 = (A2 – Aavg)/(Aavg – A1)   t1/t2 = (60 – 50)/(50 – 30) = 1/2   So out of a total of 3 parts of the journey time, she drove at 30 mph for 1 part and at 60 mph for 2 parts of the time. Fraction of the total time for which she drove at 30 mph is 1/3.   ANSWER (The average speed is 1/3 miles per hour.)
<result>B</result>
Myra drove at an average speed of 30 miles per hour for some time and then at an average speed of 60 miles/hr for the rest of the journey. If she made no stops during the trip and her average speed for the entire journey was 50 miles per hour, for what fraction of the total time did she drive at 30 miles/hour?