Question 66

The speed of a motor-boat in still water and the speed of the current of water is 20 km/h and 4 km/h respectively. To go a certain distance along the current the boat takes 4 hours. Find the time taken by the boat to cover the same distance against the current.

Solution

The speed of a motor-boat in still water and the speed of the current of water is 20 km/h and 4 km/h respectively.

To go a certain distance along the current the boat takes 4 hours.

$$\frac{distance}{20+4} = 4$$

$$\frac{distance}{24} = 4$$

distance = 96 km

Time taken by the boat to cover the same distance against the current = $$\frac{96}{20-4}\ $$

= $$\frac{96}{16}\ $$

= 6 hours

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