The following question has three statements. Study the question and the statements and decide which of the statement(s) is/are necessary to answer the question. What is the speed of boat in still water? Statement I: The boat can cover 25 km downstream distance in 5 hours. Statement II: Speed of the stream is two-third of the speed of boat in still water. Statement III: The boat can cover 25 km upstream distance in 10 hours.

We need two equations to find boat speed (b) and stream speed (s). Downstream speed = b + s = 25/5 = 5 kmph. Upstream speed = b - s = 25/10 = 2.5 kmph. Statement II: s = (2/3)b. I & III: 5 and 2.5 give b = 3.75, s = 1.25. Check II: (2/3)×3.75 = 2.5 ≠ 1.25, so II is inconsistent. I & II: b + (2/3)b = 5, gives b = 3, s = 2. III & II: b - (2/3)b = 2.5, gives b = 7.5, s = 5. These are inconsistent pairs, so we need exactly one consistent pair. Actually, any two statements together can solve (even if inconsistent), so option E is correct.