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A boat sails certain kilometres downstream from P to Q and sails 3/4th of the previous distance upstream. The boat takes 5 hours less to sail downstream. What distance in kilometre did the boat sail upstream if speed of boat in still water is 7.5km/hr and speed of stream is 2.5km/hr?

A boat sails certain kilometres downstream from P to Q and sails 3/4th of the previous distance upstream. The boat takes 5 hours less to sail downstream. What distance in kilometre did the boat sail upstream if speed of boat in still water is 7.5km/hr and speed of stream is 2.5km/hr? Correct Answer 75

GIVEN :

Speed of boat in still water is 7.5km/hr and speed of stream is 2.5km/hr

The boat takes 5 hours less to sail downstream.

 

ASSUMPTION :

Let distance downstream = x

⇒ Distance upstream = 3x/4

Speed of boat in still water = 7.5km/hr

Speed of stream = 2.5km/hr

 

CALCULATION :

⇒ Speed downstream = 7.5 + 2.5 = 10km/hr

⇒ Speed upstream = 7.5 – 2.5 = 5km/hr

⇒ Time taken to sail downstream = (x/10)hr

⇒ Time taken to sail upstream = (3x/20)hr

According to the question,

⇒ 3x/20 – x/10 = 5

⇒ (3x – 2x)/20 = 5

⇒ x = 100

⇒ 3x/4 = 75

∴ Distance travelled upstream is 75 km

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