1.

A boat can go 5 km upstream and 7.5 km downstream in 45 minutes. It can also go 5 km downstream and 2.5 km upstream in 25 minutes. How much time (in minutes) will it take to go 6 km upstream?1. 242. 323. 364. 30

Answer» Correct Answer - Option 3 : 36

Given:

A boat goes 5 km upstream and 7.5 km downstream in 45 minutes

Also, it goes 5 km downstream and 2.5 km upstream in 25 minutes

Concept used:

Upstream speed = Speed of the boat in still water - Speed of flow of the stream

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

Calculation:

Let the Downstream and Upstream speed be 'd' km/hr and 'u' km/hr respectively

 As per the question,

5/u + 7.5/d = 45/60     -----eq-n(1)

2.5/u + 5/d = 25/60     -----eq-n(2)

Multiplying eq-n(2) by 2 and then subtracting eq-n(1) from (2), we get

\({2.5 \over d}\) = \({5 \over 60}\)

⇒ d = 30

By putting the value of 'd' in any of the eq-n, we get the value of 'u'

⇒ u = 10

Now

Time is taken to travel 6 km upstream

= 6/10 hour or 36 minutes

∴ The time required to travel 6 km upstream is 36 minutes

 



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