Question

A motor boat whose speed is 18km/hr in Still water takes 1 hour motor go 14km upstream than to return downstream to the same spot. find speed of the stream.​

Answer 1

Answer:

The speed of stream is 12.7 km/h .

Step-by-step explanation:

Given as :

The speed of boat = x = 18 km/h

Distance cover in upstream = distance cover in downstream = 14 km

Total time to go and return =1 hour

Let The speed of stream = y km/h

According to question

Distance = Speed × time

Total Time =  $\dfrac{distance}{speed}$

or, 1 = $\dfrac{14}{x-y}$ + $\dfrac{14}{x+y}$

or, (x - y) (x + y) = 28

Or, x² - 2 x y + y² = 28

Or, 18² - 2 ×18 × y + y² = 28

Or, y² - 36 y + 296 = 0

solving the quadratic equation

y = $\dfrac{36\pm \sqrt{(-36)^{2}-4\times 1\times 296}}{2\times 1}$

∴ y = 23.29 , 12.7

So, The speed of stream = y = 12.7 km/h

Hence, The speed of stream is 12.7 km/h . Answer