Question

If a boat is moving in upstream at a speed of 28 km/hr and goes downstream at a speed of 40 km/hr, then what is the speed of the stream?
1. 34 km/hr
2. 12 km/hr
3. 6 km/hr
4. 18 km/hr

Answer 1

Correct Answer - Option 3 : 6 km/hr

Given:

Upstream speed = 28 km/hr

Downstream speed = 40 km/hr

Concept Used:

Upstream speed = (x – y) km/hr

Downstream speed = (x + y) km/hr

where,

x is the speed of a boat in still water.

y is the speed of a stream.

Calculation:

⇒ x + y = 40      ----(1)

⇒ x – y = 28      ----(2)

Adding both the equation we get,

⇒ 2x = 68

⇒ x = 34

Putting the above value in equation 1,

⇒ 34 + y = 40

⇒ y = 40 – 34

⇒ y = 6

∴ The speed of stream is 6 km/hr.