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F.5 Maths difficult quuestion

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A cruise ship set off from town a at 6 a.m. It travelled 840 km downstream to town B and then travelled upstream back to town A. It took 37 hours 30 minutes for the whole journey. Given that the speed of the current was 3 km/h, find the time when the cruise ship arrived at town B. Ans: 11:30 p.m.

最佳解答:

let the average speed of ship be x km/h 840/ (x+3) +840/(x-3) =37.5 840x+2520+840x-2520=37.5(x^2-9) 37.5x^2-1680x-337.5=0 x=-0.2(rejected/0 or 45 so the time requried= 840/48=17.5hr 6.am +17.5hr=11:30pm

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