Points X, Y, and Z lie, in that order, on a straight railroad track. The distance from point X to point Y is twice the distance from point Y to point Z. A train traveled from point X to point Z without stopping. The train's average speed when traveling from point X to point Y was 300 miles per hour and the train's average speed when traveling from point Y to point Z was 100 miles per hour. What was the train's average speed, in miles per hour, when traveling from point X to point Z?	Choose the correct answer:
A) 200	B) 220	C) 240	D) 180	E) 260
Average speed = distance/time   Because we are looking for average speed we can pick a distance for the variable D.   Speed X-Y = 300   Speed Y-Z = 100   Average Speed = total distance/total rate   rate = distance/time   X====================Y==========Z   If X-Y is twice the length of Y-Z then let X-Y = 2d and let Y-Z= d   Average speed = 3d/(2d/300) + (d/100)   3d/(2d/300) + (3d/300)   3d/(5d/300)   900d/5d   Average speed = 180   ANSWER: 180900 /5= 
<gadget id="calculator">900 /5</gadget>
<output>180</output>
180   ANSWER: 180
<result>D</result>
Points X, Y, and Z lie, in that order, on a straight railroad track. The distance from point X to point Y is twice the distance from point Y to point Z. A train traveled from point X to point Z without stopping. The train's average speed when traveling from point X to point Y was 300 miles per hour and the train's average speed when traveling from point Y to point Z was 100 miles per hour. What was the train's average speed, in miles per hour, when traveling from point X to point Z?