The ratio of speed of boat in still water to the speed of stream is 5

1.	The ratio of speed of boat in still water to the speed of stream is 5 : 2. It takes 4 hour more to travel 42 km upstream than to travel same distance downstream. Find the speed of boat in still water.1. 12 km/hr2. 10 km/hr3. 15 km/hr4. 20 km/hr5. 17 km/hr
Answer» Correct Answer - Option 2 : 10 km/hr Solution: Let the speed of boat in still water be u km/hr and the speed of the stream is v km/hr. Given: u : v = 5 : 2 Formula Used: Speed while travelling downstream = u + v Speed while travelling upstream = u - v Calculations: Let u = 5x and v = 2x Speed while travelling downstream = 5x + 2x = 7x Speed while travelling upstream = u-v = 5x - 2x = 3x Time(upstream) = 42/3x and Time(downstream) = 42/7x It is given that it takes 4 hour more to travel 42 km upstream than to travel same distance downstream. ⇒ 42/3x = 42/7x +4 ⇒ 14/x = 6/x + 4 ⇒ 8/x = 4 ⇒ x = 2 Speed in still water = u = 5x ⇒ 5 × 2 = 10 km/hr

The ratio of speed of boat in still water to the speed of stream is 5 : 2. It takes 4 hour more to travel 42 km upstream than to travel same distance downstream. Find the speed of boat in still water.1. 12 km/hr2. 10 km/hr3. 15 km/hr4. 20 km/hr5. 17 km/hr

Answer» Correct Answer - Option 2 : 10 km/hr

Solution:

Let the speed of boat in still water be u km/hr and the speed of the stream is v km/hr.

Given:

u : v = 5 : 2

Formula Used:

Speed while travelling downstream = u + v

Speed while travelling upstream = u - v

Calculations:

Let u = 5x and v = 2x

Speed while travelling downstream = 5x + 2x = 7x

Speed while travelling upstream = u-v = 5x - 2x = 3x

Time(upstream) = 42/3x and Time(downstream) = 42/7x

It is given that it takes 4 hour more to travel 42 km upstream than to travel same distance downstream.

⇒ 42/3x = 42/7x +4

⇒ 14/x = 6/x + 4

⇒ 8/x = 4

⇒ x = 2

Speed in still water = u = 5x

⇒ 5 × 2 = 10 km/hr

Discussion

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