A train travels from city C to city D. 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? Choose the correct choice from the following answers.
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   C.........90........3..........270   D.........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 C to city D. 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?