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    Question

    Some students went on a field trip. At a speed of 6

    km/h, they traveled by bike for 2 hours then at a speed of 2 km/h, they walked for another hour; then they rested for an hour and had lunch for half an hour; then at a speed of 1 m/s, they walked for an hour to visit a garden; and finally at a speed 4 km/h, they returned home in 3 hours. Their average speed, in km/h,(rounded off to two places of the decimal) is:
    A 9.96 km/h Correct Answer Incorrect Answer
    B 3.48 km/h Correct Answer Incorrect Answer
    C 4.42 km/h Correct Answer Incorrect Answer
    D 7.28 km/h Correct Answer Incorrect Answer

    Solution

    Biking Phase- Speed: 6 km/h Time: 2 hours Distance traveled = Speed × Time = 6 km/h × 2 hours = 12 km   Walking Phase-   Speed: =2 km/h   Time: = 1 hour Distance traveled = Speed × Time = 2 km/h × 1 hour = 2 km Rest and Lunch Phase- Time: 1 hour for rest + 0.5 hours for lunch = 1.5 hours      Since there's no movement, this time adds to the total time but not to the distance. Garden Visit Phase-   Speed: 1 m/s (which needs to be converted to km/h for consistency). Since 1 m/s = 3.6 km/h,     Distance traveled = Speed × Time = 3.6 km/h × 1 hour = 3.6 km Returning Home Phase-    Speed: 4 km/h     Time: 3 hours     Distance traveled = Speed × Time = 4 km/h × 3 hours = 12 km   Total Distance Traveled = 12 km (Biking) + 2 km (Walking) + 3.6 km (Garden Visit) + 12 km (Returning Home) = 29.6 km   Total Time Spent (including resting and lunch breaks) = 2 hours (Biking) + 1 hour (Walking) + 1.5 hours (Rest and Lunch) + 1 hour (Garden Visit) + 3 hours (Returning Home) = 8.5 hours   Average Speed = Total Distance Traveled / Total Time Spent Average Speed = 29.6 km / 8.5 hours ≈ 3.48 km/h

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