Question

The speed of a boat in still water is 9 km/h. A boat goes
72 km and back to its starting point in 18 hours. Find the
speed of stream?
(a) 3 km/hr (b) 4 km/hr
c) 6km/hr
​

Answer 1

Answer:

Speed=d/t=72/18=4km/hr

Answer 2

Answer:

According to the question, correct option is (a) 3 km/hr

Step-by-step explanation:

Let, the speed of the stream = x kmph

From the given data,

 72/9+x + 72/9−x = 18 hrs

=>  (9-x) 72 + (9+x) 72 = 18 (9+x) (9-x)

=>  648 - 72x + 648 + 72x = 18 ( 9² - x²)

=>  1296 = 1498 - 18x²

=> x² = 162/18

=> x² = 9

=> x = 3 kmph

Therefore, the speed of the stream = 3 kmph