A man can row 6 km/h in still water. If it takes him twice as long to row upstream as to row downstream of a river, then the speed of the stream is: MCQ with Answer and Explanation
Two cars leave a location simultaneously at a right angle to each other. Their speeds are 36 km/h and 48 km/h respectively. Find the direct distance between them after 15 minutes.
Explanation:
Time = 15 minutes = 0.25 hours. Distance covered by first car = 36 * 0.25 = 9 km. Distance covered by second car = 48 * 0.25 = 12 km. Since they travel at right angles, distance between them = sqrt(9^2 + 12^2) = sqrt(81 + 144) = sqrt(225) = 15 km.
Explanation:
Let original speed be s. 180 / (s - 5) - 180 / s = 1 => 180(5) = s(s - 5) => 900 = s(s - 5). Solving s^2 - 5s - 900 = 0 gives (s - 30)(s + 25) = 0. Since speed is positive, s = 30 km/h.
The speed of a boat in still water is 14 km/h and the speed of the current is 4 km/h. How much time will the boat take to cover a distance of 72 km downstream?
Explanation:
Downstream speed = Speed in still water + Speed of current = 14 + 4 = 18 km/h. Time taken = Distance / Downstream speed = 72 / 18 = 4 hours.
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