A train travels from city A to city B. The average speed of the train is 60 miles/hr and it travels the first quarter of the trip at a speed of 90 mi/hr. What is the speed of the train in the remaining trip?  Select the correct option:  A) 30  B) 45  C) 54  D) 72  E) 90
Using the RTD chart, with A being the first quarter, B the rest of the trip and All the combinedtrip.   _______R_____T______D   A.........90........3..........270   B.........54.......15.........810   All........60.......18........1080   Let me explain how we fill in the chart:   1) Starting with what we know, we add 90 and 60   2) Picking an easy number for the total distance (6*9=54), so I chose 540. Multiply by 2 to get the whole trip, and we get 1080. Add 1080 for all-distance.   3) 1/4 of the whole distance happened at a Rate of 90. So, 1080/4=270, add 270 under A-D.   4) 2080 - 270 = 810, for the rest of the trip. Add 810 under B-D.   5) Claculate the individual Times for A and All, using T=D/R. Add the results, 3 and 18, under A-T and All-T.   6) 18-3=15, this is the remaining Time for B. Add 15 under B-T.   7) Finally, 15R=810 --&gt;R=810/15 --&gt; R= 54ANS 54
<result>C</result>
A train travels from city A to city B. The average speed of the train is 60 miles/hr and it travels the first quarter of the trip at a speed of 90 mi/hr. What is the speed of the train in the remaining trip?