Question

The speed of water in a river is 4 kmph and the speed of boat in still water is 8 kmph. If
the same boat is used to travel a distance of 16 km in the river from A to B down stream
and back from B to A. Find the total time taken by the boat.​

Answer 1

Answer:

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Answer 2

Answer:

$t = 5.33 hr$

Explanation:

$V_w : \texttt{\blue{velocity \:of\: water}}$

$V_b : \texttt{\blue{velocity \:of\: boat}}$

$V_{bw}: \texttt{\red{velocity \:of\: boat\: with \: respect\: to water}}$

Given:

$V_w = 4kmph$

$V_b = 8 kmph$

d = 16km

To Find

time taken

Solution

Time taken in travelling downstream

$V_{bw} = 8+4 = 12kmph$

$t =\dfrac{d}{ V_{bw}}$

$t_1 =\dfrac{16}{ 12}$

$t_1 =\dfrac{4}{ 3} hr$

Time taken in travelling upstream

$V_{bw} = 8-4= 4kmph$

$t =\dfrac{d}{ V_{bw}}$

$t_2 =\dfrac{16}{4}$

$t_2 = 4 hr$

Total time taken

$t=t_1+t_2$

$t =\dfrac{4}{ 3} +4$

$t =\dfrac{4+12}{ 3}$

$t =\dfrac{16}{ 3}$

$t = 5.33 hr$