Question

In New York there is a long straight avenue through the city, there are three speed limit signs. THEY occur in the following order : 60, 30, and 15 km /h, with the 30 km/h sign being midway between the other two. Obeying these speed limits, the smallest possible time Oc that a driver can spend on this part of the road is to travel between the first and second signs at 60 km/h and between the second and third signs at 30 km/h. Another way of following the required speed limit is that a driver could slow down from 60 to 30 km/h with a constant deceleration and then do a similar thing from 30 to 15 km/h. This alternative requires a time Od. Find the ratio Od/Oc