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The ratio of speed of the boat to that of the current is 7 : 3. If the boat goes downstream in 6 hrs 20 minutes, then it will return in -

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Question

The ratio of speed of the boat to that of the current is 7 : 3. If the boat goes downstream in 6 hrs 20 minutes, then it will return in

Options

  • 6 hrs 50 min

  • 8 hrs 40 min

  • 10 hrs 20 min

  • None of these

MCQ

Solution

None of these

Explanation:

Method-1: Let distance covered upstream = d km 6 hrs 20 minutes = 380 minutes

So, `d/(7x + 3x)` = 380

⇒ d = 3800 x

We have to find time taken to travel upstream

i.e. t = `d/(7x - 3x)`, t = `(3800 x)/(4x)`

= 950 minutes

= `15 50/60`

= 15 hrs 50 minutes.

Method-2: Shorter method is, Ratio of upstream speed : downstream speed

= (7x – 3x): (7x + 3x)

= 4x : 10x

= 2 : 5

Ratio of time upstream Downstream would be 5 : 2

⇒ `x/380 = 5/2`

⇒ `x = (380 xx 5)/2`

= 950 min

= 15 hrs 50 minutes.

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Time, Speed and Distance (Entrance Exam)
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