The following questions are accompanied by three statement I, II and III. You have to determine which statement(s) is/are necessary/sufficient to answer the question. Find the value of y (in km). (I) The speed of current is 1.5 km/hr. (II) He covers a distance of 60 km downstream in 5 hours. (III) He covers the distance of y km downstream in 3 hours.

Boat and stream problem. To find y km distance covered downstream in 3 hours, we need the downstream speed. From II: 60 km in 5 hours downstream, so downstream speed = 12 km/hr. From III: y km in 3 hours downstream, so y = 12 * 3 = 36 km. Statement I (current speed = 1.5 km/hr) is unnecessary - we don't need to separate boat speed and current speed. Therefore II & III together are sufficient. Answer D is correct.