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 200 miles per hour and the train's average speed when traveling from point B to point C was 150 miles per hour. What was the train's average speed, in miles per hour, when traveling from point A to point C? Options
A) 150	B) 200	C) 180	D) 190	E) 250
Average speed = distance/time   Because we are looking for average speed we can pick a distance for the variable d.   Speed A-B = 200   Speed B-180 = 150   Average Speed = total distance/total rate   rate = distance/time   A====================B==========180   If A-B is twice the length of B-180 then let A-B = 2d and let B-180 = d   Average speed = 3d/(2d/200) + (d/150)   3d/(6d/600) + (4d/600)   3d/(10d/600)   1800d/10d   Average speed = 180   ANSWER: 1801800 /10= 
<gadget id="calculator">1800 /10</gadget>
<output>180</output>
180   ANSWER: 180
<result>C</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 200 miles per hour and the train's average speed when traveling from point B to point C was 150 miles per hour. What was the train's average speed, in miles per hour, when traveling from point A to point C?