Question

The speed of a boat in still water is 12 km/h. If the boat covers a distance of 38 km upstream in 4 hours, then the speed of the stream (in km/h) is:

• A. 6.5
• B. 3.17
• C. 2.5
• D. 3

Answer 1

Answer:

C. 2.5

Given,

The Speed of the boat in still water = 12 km/hr

Boat covers the distance of 38 km upstream in 4 hrs.

Formula:

Speed = $\frac{Distance}{Time}$

If speed of boat in still water and stream be x km/hr and y km/hr respectively,

Upstream speed = (x – y) km/hr

Downstream speed = (x + y) km/hr

Calculation:

Let the speed of stream be x km/hr

Upstream speed = (12 – x) km/hr

According to the question

(12 – x) = $\frac{38}{4}$

⇒ (12 – x) × 4 = 38

⇒ 48 – 4x = 38

⇒ 4x = 48 – 38

⇒ 4x = 10

⇒ x = $\frac{10}{4}$

⇒ x = 2.5 km/hr

∴ Speed of the stream is 2.5 khm/r