The speed of a motor-boat is that of the current of water as 36 : 5. The boat goes along with the current in 5 hours 10 minutes. It will come back in?Options5 hours 50 minutes6 hours6 hours 50 minutes12 hours 10 minutes

The speed of the boat in still water (b) to the speed of the current (c) is given as 36:5. This means that the speed of the boat in still water is 36x and the speed of the current is 5x.

When the boat is moving along with the current, the effective speed of the boat (E1) is the sum of the speed of the boat in still water and the speed of the current. So, E1 = b + c = 36x + 5x = 41x.

The boat takes 5 hours 10 minutes to travel a certain distance with the current. So, the distance (d) can be calculated as d = E1 * time = 41x * 5.167 (converting 5 hours 10 minutes to hours) = 211.847x.

When the boat is moving against the current, the effective speed of the boat (E2) is the difference between the speed of the boat in still water and the speed of the current. So, E2 = b - c = 36x - 5x = 31x.

The time it will take for the boat to travel the same distance against the current can be calculated as time = d / E2 = 211.847x / 31x = 6.83 hours, which is approximately 6 hours 50 minutes.

So, the boat will come back in approximately 6 hours 50 minutes. The correct option is 6 hours 50 minutes.