A boat covers 196 km downstream in 7 hours when the speed of the stream is x km/hr. The same boat covers 180 km upstream in 9 hours when the speed of the stream is (x + 2) km/hr. If the speed of the boat in still water is increased by 40%, find the time taken by the boat to cover 351 km downstream when the speed of the stream is (x + 1) km/hr.

ATQ, The downstream speed of the boat when the speed of the stream is x km/hr = 196/7 = 28 km/hr The upstream speed of the boat when the speed of the stream is (x + 2) km/hr = 180/9 = 20 km/hr Let the speed of the boat in still water be S km/hr. Then, S = 28 – x ...(i) S = 20 + (x + 2) ...(ii) From (i) and (ii), 28 – x = 20 + x + 2 28 – x = 22 + x 2x = 6 x = 3 The speed of the boat in still water = 28 – 3 = 25 km/hr The new speed of the boat in still water (increased by 40%) = 25 * 140/100 = 35 km/hr The downstream speed of the boat when the speed of the stream is (x + 1) km/hr = 35 + x + 1 = 35 + 3 + 1 = 39 km/hr Required time taken = 351/39 = 9 hours