Problem: The rails on a railroad are feet long. As the train passes over the point where the rails are joined, there is an audible click. The speed of the train in miles per hour is approximately the number of clicks heard in:
Answer Choices:
A. seconds
B. minutes
C. minutes
D. minutes
E. none of these
Solution:
30 ft per second corresponds to 1 click per second. In miles per hour, corresponds to 1 click per second. 1 mph corresponds to clicks per second, which is approximately 1 click in 20 seconds. So miles per hour corresponds approximately to clicks in 20 seconds.