Question

A motor boat goes down the stream 30 km and again returns to the
starting point in a total time of 4 hours and 30 minutes. If the speed of the
stream is 5 km/hr, then find the speed of the motor boat in still water.​

Answer 1

Answer:

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 - x) km/hr.

30 + 30 = 4 1

(15 + x) (15 - x) 2

900 = 9

225 - x2 2

9x2 = 225

x2 = 25

x = 5 km/hr

Answer 2

The speed of motor boat in still water is $\dfrac{5}{3}\ km/hr$

Step-by-step explanation:

Since we have given that

Distance = 30 km

Speed of stream = 5 km/hr

Let the speed of motor boat in still water be 'x'.

According to question, we get that

$\dfrac{30}{x-5}+\dfrac{30}{x+5}=4\dfrac{1}{2}\\\\\dfrac{30}{x-5}+\dfrac{30}{x+5}=\dfrac{9}{2}\\\\\dfrac{x-5+x+5}{x^2-25}=\dfrac{9}{2\times 30}=\dfrac{3}{2\times 10}=\dfrac{3}{20}\\\\\dfrac{2x}{x^2-25}=\dfrac{3}{20}\\\\20\times 2x=3(x^2-25)\\\\40x=3x^2-75\\\\3x^2+40x-75=0\\\\x=-5,\dfrac{5}{3}$

Hence, the speed of motor boat in still water is $\dfrac{5}{3}\ km/hr$

# learn more:

A motor boat goes down the stream 30 km and again returns to the

starting point in a total time of 4 hours and 30 minutes. If the speed of the

stream is 5 km/hr, then find the speed of the motor boat in still water.​

https://brainly.in/question/15702947