Question

3) Guddi's swimming speed in still water to the speed of river is 7:1. She swims 4.2 km up the river in just 14 min.
How much time will Guddi take to swim 18.4 km down the river?​

Answer 1

Answer:

$\boxed{\sf \: Time \:taken \:in \: down \: the \: river \: to \: cover \: 18.4 \: km \: = 46 \: min \: }$

Step-by-step explanation:

Given that, Guddi's swimming speed in still water to the speed of river is 7 : 1.

Let assume that speed of swimming in still water be 7x km per hr

Speed of river be x km per hr

So,

Speed in upstream = 7x - x = 6x km per min

Speed of downstream = 7x + x = 8x km per min

Now, given that She swims 4.2 km up the river in just 14 min.

So,

Distance covered in upstream = 4.2 km

Time taken in upstream = 14 min

Speed of upstream = 6x km per hour

We know,

$\sf \: Distance = Speed \times Time$

$\sf \:4.2 = 6x \times \dfrac{14}{60}$

$\sf \:x = \dfrac{4.2 \times 60}{7 \times 6}$

$\sf \:x = \dfrac{42 \times 6}{14 \times 6}$

$\implies\sf \: x = 3$

Now, we have to find how much time will Guddi take to swim 18.4 km down the river.

So, we have

Distance covered in downstream = 18.4 km

Speed of downstream = 8x km per hour

We know

$\sf \: Time = \dfrac{Distance}{Speed}$

$\sf \: Time = \dfrac{18.4}{8x}$

$\sf \: Time = \dfrac{18.4}{8 \times 3} \: hours$

$\sf \: Time = \dfrac{18.4}{8 \times 3} \times 60 \: min$

$\sf \: Time = \dfrac{184}{8 \times 3} \times 6 \: min$

$\sf \: Time = \dfrac{184}{8 \times 1} \times 2 \: min$

$\sf \: Time = \dfrac{184}{4} \: min$

$\implies\boxed{\sf \: Time \:taken \:with \: river \: to \: cover \: 18.4 \: km \: = 46 \: min \: }$