A boatman rows 20 km downstream in 2 hours and covers the same distance upstream in 4 hours. Find the speed of the boat in still water. MCQ with Answer and Explanation

Explanation:
Let original speed be s. 360/s - 360/(s+10) = 3. Dividing by 3: 120/s - 120/(s+10) = 1. 120(s + 10 - s) = s(s + 10) => 1200 = s(s + 10). Solving s^2 + 10s - 1200 = 0 gives (s-30)(s+40) = 0. Since speed is positive, s = 30 km/h.

Explanation:
Let stream speed be c. Upstream speed = 12 - c, Downstream speed = 12 + c. Given: 2 * (12 - c) = 12 + c => 24 - 2c = 12 + c => 3c = 12 => c = 4 km/h.

Explanation:
By 6:00 AM, the first man has traveled for 2 hours, covering 5 * 2 = 10 km. Relative speed = 7 - 5 = 2 km/h. Time to meet = 10 / 2 = 5 hours. Meeting time = 6:00 AM + 5 hours = 11:00 AM.