the speed of boat in still water is 25 km/hr and speed of current is 7km/hr .If a boat goes from place A to place B and return from B to A and it takes 6 hours 40 minutes in total.Find the time taken by boat to cover the twice the distance of AB downstream

Ans kya he

24/5 =4.8 hr

Speed of boat in still water, a = 25km/h Speed of stream, b = 7km/h Speed of boat going downstream, su = a+b = 25+7 = 32km/h = 8.88m/s Speed of boat going upstream, sd = a-b = 25-7 = 18km/h = 5m/s Now, s=d/t Distance, d = AB = BA So, su=d/t1 and sd=d/t2 Which implies, su•t1 = sd•t2 . . . . (1) Also, t1+t2 = 6h40m = 6.66h => t1 = 6.66 - t2 Substituting the values in (1), 18 x (6.66-t2) = 32 x t2 => t2 = 2.39h Now, time for 2xAB downstream = 2 x t2 = 4.79h = 4h47m