Question

the speed of a boat in still water is 15 km per hour it can go 45 km upstream and return downstream to the original point in 6 hours and 45 minutes find the speed of the stream

Answer 1

Let the speed of the stream be xkm/hr.

Given that Speed of the boat in still water = 15 km/hr.

Speed of the boat upstream = (15 - x).

Speed of the boat downstream = (15 + x).

Given that it return downstream to the original point in 6 hours 45 minutes.

$= \ \textgreater \ \frac{45}{15 - x} + \frac{45}{15 + x} = 6 \frac{45}{60}$

$= \ \textgreater \ \frac{45}{15 - x} + \frac{45}{15 + x} = 6 \frac{3}{4}$

$= \ \textgreater \ \frac{45}{15 - x} + \frac{45}{15 + x} = \frac{27}{4}$

$= \ \textgreater \ \frac{180}{15 - x} + \frac{180}{15 + x} = 27$

$= \ \textgreater \ \frac{5400}{15^2 - x^2} = 27$

$= \ \textgreater \ \frac{5400}{225 - x^2} = 27$

= > 5400 = 27(225 - x^2)

= > 5400/27 = 225 - x^2

= > 200 = 225 - x^2

= > -x^2 = -25

= > x^2 = 25

= > x = +5,-5


The speed of the stream cannot be negative.

Therefore the speed of the stream will be 5km/hr.



Hope this helps!

Answer 2

Answer:

please see the attachment