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Question

The speed of a stream is 3 km/h and the speed of a man in still water is 6 km/h. The time taken by the man to swim 37 km downstream is:

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$4\frac{1}{9} \text{ h}$

Solution: Downstream Swim Time Calculation

This section details the calculation for the time taken to swim downstream, using the provided speeds and distance.

Given Information

  • Speed of stream ($v_s$) = 3 km/h
  • Speed of man in still water ($v_m$) = 6 km/h
  • Distance downstream ($d$) = 37 km

Calculating Downstream Speed

To find the speed while swimming downstream, we add the speed of the man in still water to the speed of the stream.

Downstream speed ($v_d$) is calculated as: $v_d = v_m + v_s$

Substituting the given values: $v_d = 6 \text{ km/h} + 3 \text{ km/h} = 9 \text{ km/h}$

Calculating Time Taken

The time taken to travel a certain distance is found by dividing the distance by the speed.

Time $= \frac{\text{Distance}}{\text{Speed}}$

Using the downstream speed and distance:

Time $= \frac{d}{v_d} = \frac{37 \text{ km}}{9 \text{ km/h}}$

Time $= \frac{37}{9}$ hours

Converting to Mixed Fraction

To express the time as a mixed fraction:

Divide 37 by 9: $37 \div 9 = 4$ with a remainder of $1$.

So, the time is $4 \frac{1}{9}$ hours.

Final Result

The time taken by the man to swim 37 km downstream is $4 \frac{1}{9}$ hours.

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Important Questions from Boat and River

  1. A boat goes 30 km upstream in 3 hours and downstream in 1 hour. How much time (in hours) will this boat take to cover 60 km in still water?

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  3. The time taken by a boat to travel 13 km downstream is the same as time taken by it to travel 7 km upstream. If the speed of the stream is 3 km/h, then how much time (in hours) will it take to travel a distance of 44.8 km in still water?

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