Question

Johnny can row at 5 kmph in still water. If the velocity of the current is 1 kmph and it takes him 1 hour to row to the supply ship and come back, how far is the supply ship?

Answer 1

Let the distance between Johnny and supply ship be d km.

Velocity of the Johnny in still water = 5 kmph.

Velocity of the current = 1 kmph.

∴ Velocity by which Johny wil go = 5 + 1

= 6 kmph.

∴ Time taken by it (t₂) = d/6

In second case,

Velocity = 5 - 1

= 4 kmph.

∴ Time taken (t₂) = d/4

∵ t₁ + t₂ = 1

∴ d/6 + d/4 = 1

⇒ (2d + 3d)/12 = 1

⇒ 5d = 12

∴ d = 2.4 km.

∴ Distance between the Johnny and the Supply ship is 2.4 km.

Hope it helps.