1.

A ship sails 25 km of a river towards downstream in 5 hours. If the speed of boat is 1.5 times the speed of current, then find the time taken by ship to cover the same distance upstream.1. 25 hours2. 30 hours3. 21 hours4. 24 hours

Answer» Correct Answer - Option 1 : 25 hours

Given:

Downstream distance = 25 km

Time taken = 5 hours

Speed of Boat : Speed of current = 3 : 2

Formula Used:

Speed = Distance/Time

D = B + S

U = B - S

where, D → Downstream speed, U → Upstream speed, B → Speed of boat in still water, S → Speed of stream.

Calculations:

Let the speed of boat and speed of stream be 3x and 2x respectively.

Speed = Distance/Time

⇒ D = 25/5

⇒ D = 5 km/hr

Now, D = B + S

⇒ 5 = 3x + 2x

⇒ 5 = 5x

⇒ x = 1

B = 3x = 3 × 1

⇒ B = 3 km/hr

Similarly, 

S = 2x = 2 × 1

⇒ S = 2 km/hr

Now, U = B - S

⇒ U = 3 - 2 = 1 km/hr

Speed = Distance/Time

⇒ 1 = 25/Time

⇒ Time = 25 hours

∴ The time taken by ship to cover 25 km upstream is 25 hours.



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