A man can row 7.5 km/h in still water, if the speed of the river is 1.5 km/h. It takes him 50 mins to go to that place and back to the starting point. Find the distance.

- 5 km
- 3 km
- 2 km
- 4 km

Option 2 : 3 km

**Given**:

The speed of a man in still water = 7.5 km/h

The speed of the river = 1.5 km/h

Time taken to go to that place and back to the starting point = 50 minutes.

**Formula**:

1) Upstream = (u - v) km/h, where “u” is the speed of the man/boat in still water and “v” is the speed of the stream

2) Downstream = (u + v) km/h, where “u” is the speed of the man/boat in still water and “v” is the speed of the stream.

3) Time = Distance/Speed

**Calculation**:

Let the required distance be “x” km,

According to the formula,

Downstream speed = (7.5 + 1.5) = 9 km/h

Upstream speed = (7.5 - 1.5) = 6 km/h

According to the third formula,

(x/9) + (x/6) = 50/60

⇒ (2x + 3x)/18 = 5/6

⇒ (5x)/18 = 5/6

⇒ 30x = 90

⇒ x = 3 km.

**∴**** The distance between the places is 3 km. **

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