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

Let the speed of the boat is u km/h

Then,

30/(15+u)+30/(15-u)=4.5

30*30/(225-u*u)=4.5

225-u*u=200

u=5km/h

Answer 2

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

▶Speed downstream = (15 + x) km/hr,
▶Speed upstream = (15 - x) km/hr.

▶30/(15 + x)➕30/(15 - x)=> 4 1/2

▶900/ 225 - x^2 2=> 9/2

▶ 9x^2 = 225
▶ x^2 = 25

 x = 5 km/hr....✔✔✔