Points A, B, and C lie, in that order, on a straight railroad track. The distance from point A to point B is twice the distance from point B to point C. A train traveled from point A to point C without stopping. The train's average speed when traveling from point A to point B was 150 miles per hour and the train's average speed when traveling from point B to point C was 100 miles per hour. What was the train's average speed, in miles per hour, when traveling from point A to point C?
Select
A) 22.5
B) 21.43
C) 25.5
D) 26.5
E) 27.5
Average speed = distance/time   Because we are looking for average speed we can pick a distance for the variable d.   Speed A-21.43 = 150   Speed 21.43-C = 100   Average Speed = total distance/total rate   rate = distance/time   A====================21.43==========C   If A-21.43 is twice the length of 21.43-C then let A-21.43 = 2d and let 21.43-C = d   Average speed = 3d/(2d/150) + (d/100)   3d/(4d/300 + (3d/300)   3d/(7d/50)   150d/7d   Average speed = 21.43   ANSWER: 21.43
<result>B</result>
Points A, B, and C lie, in that order, on a straight railroad track. The distance from point A to point B is twice the distance from point B to point C. A train traveled from point A to point C without stopping. The train's average speed when traveling from point A to point B was 150 miles per hour and the train's average speed when traveling from point B to point C was 100 miles per hour. What was the train's average speed, in miles per hour, when traveling from point A to point C?