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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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