The speed of a boat downstream is 18 km/h and upstream is 12 km/h. How much distance can the boat cover in still water in 3 hours? MCQ with Answer and Explanation
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Question #1
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The speed of a train is 20% more than the speed of a car. Both start from city P at the same time and reach city Q, 120 km away, at the same time. On the way, the train stops for 10 minutes at various stations. What is the speed of the car?
Correct Answer: Option D
Explanation:
Let car speed be c, then train speed is 1.2c. Time difference = 120/c - 120/(1.2c) = 10/60 hour = 1/6 hour. 120/c * (1 - 1/1.2) = 1/6 => 120/c * (0.2/1.2) = 1/6 => 120/c * (1/6) = 1/6 => c = 120 km/h.
Let car speed be c, then train speed is 1.2c. Time difference = 120/c - 120/(1.2c) = 10/60 hour = 1/6 hour. 120/c * (1 - 1/1.2) = 1/6 => 120/c * (0.2/1.2) = 1/6 => 120/c * (1/6) = 1/6 => c = 120 km/h.
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Maths
Time Speed and Distance
Question #2
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A car covers a distance of 450 km at a certain speed. If the speed is increased by 5 km/h, it takes 1 hour less to cover the same distance. Find the original speed of the car.
Correct Answer: Option D
Explanation:
Let original speed be s. 450/s - 450/(s+5) = 1 => 450(s + 5 - s) = s(s + 5) => 2250 = s(s + 5). Solving s^2 + 5s - 2250 = 0 gives (s - 45)(s + 50) = 0. Since speed is positive, s = 45 km/h.
Let original speed be s. 450/s - 450/(s+5) = 1 => 450(s + 5 - s) = s(s + 5) => 2250 = s(s + 5). Solving s^2 + 5s - 2250 = 0 gives (s - 45)(s + 50) = 0. Since speed is positive, s = 45 km/h.
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Maths
Time Speed and Distance
Question #3
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A train 100 meters long passes an extension platform 300 meters long in 20 seconds. What is the speed of the train in km/h?
Correct Answer: Option D
Explanation:
Total distance = 100 + 300 = 400 meters. Speed = 400 / 20 = 20 m/s. In km/h = 20 * (18/5) = 72 km/h.
Total distance = 100 + 300 = 400 meters. Speed = 400 / 20 = 20 m/s. In km/h = 20 * (18/5) = 72 km/h.
This question belongs to:
Maths
Time Speed and Distance
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