Let the speed of the stream be x km/hr.
∴ Speed of the boat upstream = (18 – x) km/hr.
Speed of the boat downstream = (18 + x) km/hr.
Time taken for going 24 km upstream =
Time taken for going 24 km downstream =
According to given condition,
∴
Using the quadratic formula, we get
Since x is the speed of the stream, it cannot be negative. So, we ignore the root x = –54. Therfore, x = 6 gives the speed of the stream as 6km/h. is rejected.
Hence, the speed of the stream is 2 km/hr.