Question

The speed of a boat in still water is 8 km / hr. It can go 15 km upstream and 22 km downstream in 5 hours. Find the speed of the stream.

Answer 1

Speed of the stream = 3 Km/hr

Step-by-step explanation:

Given: The speed of a boat in still water is 8 km / hr. It can go 15 km upstream and 22 km downstream in 5 hours.

Find: Speed of the stream.

Solution:

Let speed of boat in still water be x km/hr.

and speed of the stream be y km/hr.

Then Upstream speed = (x - y) km/hr

Downstream speed = (x + y) km/hr.

Given x = 8.

15/x-y + 22/x+y = 5

Substituting x = 8, we get:

15/8-y + 22/8+y = 5

15 (8 + y ) + 22 (8-y) = 5 (8² - y²)

120 + 15y + 176 - 22y = 320 - 5y²

5y² - 7y -24 = 0

5y² - 15y +8y - 24 = 0

5y (y - 3) +8 (y - 3) = 0

(5y + 8 ) (y-3) = 0

Y = 3 or -8/5

Speed is not negative. So y = 3.

Speed of the stream = 3 Km/hr