A river 2 km wide is flowing at the rate of 2 km / h. A boatman, can row the boat at a speed of 4 km / h in still water, goes a distance of 2 km upstream and then comes back. The time taken by him to complete his journey is

Question

A river 2 km wide is flowing at the rate of 2 km / h. A boatman, can row the boat at a speed of 4 km / h in still water, goes a distance of 2 km upstream and then comes back. The time taken by him to complete his journey is (A) 60 minutes (B) 70 minutes (C) 80 minutes (D) 90 minutes

Tardigrade Admin · Accepted Answer

The velocity of upstream is (4-2) km / h and downstream is (4+2) km / h. ∴ Total time taken =(2 km /2 km / h )+(2 km /6 km / h )=80 minutes

Q. A river $2 km$ wide is flowing at the rate of $2 km / h$ . A boatman, can row the boat at a speed of $4 km / h$ in still water, goes a distance of $2 km$ upstream and then comes back. The time taken by him to complete his journey is

60 minutes

70 minutes

80 minutes

90 minutes

The velocity of upstream is $(4 - 2) km / h$ and downstream is $(4 + 2) km / h$ .
$∴$ Total time taken $= \frac{2 km}{2 km / h} + \frac{2 km}{6 km / h} = 80$ minutes

Q. A river 2km wide is flowing at the rate of 2km/h. A boatman, can row the boat at a speed of 4km/h in still water, goes a distance of 2km upstream and then comes back. The time taken by him to complete his journey is