Question

A boat whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

Answer 1

Answer:

5 km/h

Step-by-step explanation:

Assume the stream’s speed to be 5km/h .

Downstream time = 30/20 = 1.5 h

Upstream time = 30/ 10 = 3h

Total time = 4.5 hours

And our assumption is correct.

Down stream time = 30/ ( 15 + v) = a

Upstream time = 30/ ( 15 -v) = b

a + b = 30*30/ (15^2 - v^2) = 4.5

Hence,

(15^2 - v^2) = 200

v = 5 km/h

therefor speed of stream is 5km/hr