1.

A boat covered 20 km downstream and 28 km upstream. The speed of boat in still water is 7 km/hr and speed of stream is 3 km/hr. Find the time taken to complete 20 km downstream and 28 km upstream.1. 9 hours2. 8 hours3. 6 hours4. 10 hours

Answer» Correct Answer - Option 1 : 9 hours

Given:

Distance covered downstream = 20 km

Distance covered upstream = 28 km

Speed of boat in still water = 7 km/hr

Speed of stream = 3 km/hr

Concept used:

Downstream speed = Speed of boat in still water + Speed of stream

Upstream speed = Speed of boat in still water – Speed of stream

Calculation:

Downstream speed = (7 + 3) km/hr

⇒ 10 km/hr

Upstream speed = (7 – 3) km/hr

⇒ 4 km/hr

Time taken to cover 20 km downstream = 20/10 hours

⇒ 2 hours

Time taken to cover 28 km upstream = 28/4 hours

⇒ 7 hours

Total time taken to complete the whole journey = (2 + 7) hours

⇒ 9 hours

∴ The time taken to complete the whole journey is 9 hours



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