Arithmetic

Time, Speed & Distance

Medium

applied

The speed of water current is half the speed of a motor boat. The motor boat travels 15 km downstream in 1 hour. Then the time taken to return to the starting point is:

2 hours

3 hours

4 hours

4.5 hours

✅ Correct Option: 2

Let boat speed in still water $= b$ km/h and current speed $= c$ km/h.

The current speed is half the boat speed:

$c = \dfrac{b}{2}$

The boat travels 15 km downstream in 1 hour.

Downstream speed $= \dfrac{\text{Distance}}{\text{Time}}$

$= \dfrac{15}{1}$

$= 15$ km/h

Downstream speed is the sum of boat speed and current speed:

$b + c = 15$

Substituting $c = \dfrac{b}{2}$ :

$b + \dfrac{b}{2} = 15$

$\dfrac{2b + b}{2} = 15$

$\dfrac{3b}{2} = 15$

$3b = 30$

$b = 10$ km/h

Therefore:

$c = \dfrac{10}{2} = 5$ km/h

Upstream speed is the difference between boat speed and current speed:

Upstream speed $= b - c$

$= 10 - 5$

$= 5$ km/h

Time to return upstream:

Time $= \dfrac{\text{Distance}}{\text{Speed}}$

$= \dfrac{15}{5}$

$= 3$ hours

Therefore, the time taken to return to the starting point is 3 hours.

2026: 29 May Shift 2

A boat goes 24 km upstream in 4 hours and 32 km downstream in 4 hours. The speed of the boat in still water is:

2025: 21 May Shift 2

A boat can row at the speed of 16 km/hr in still water. If the river is flowing at 8 km/hr, and it takes 8 hours for a round trip, then the distance between the two places is:

2025: 16 May Shift 1

A boat covers 32 km upstream and 36 km downstream in 7 hours. Also, it covers 40 km upstream and 48 km downstream in 9 hours. The speed of the boat in still water is:

2025: 14 May Shift 2

A person can row a boat at 5 km/hr in still water. If the speed of water current in a river is 1 km/hr, and it takes him 1 hour to row to a place and come back, how far off is the place?

2026: 25 May Shift 1

In a race of 800 m, A beats B by 80 m and in a race of 600 m, B beats C by 40 m. Then A will beat C in a race of 1000 m by :

2025: 19 May Shift 1

A steamer can row at the speed of 16km/hr in still water. If the river is flowing at 8 km/hr and it takes 12 hours for a round trip, then the distance between the two places is:

The speed of water current is half the speed of a motor boat. The motor boat travels 15 km downstream in 1 hour. Then the time taken to return to the starting point is:

Solution

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