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:

Ответ:

The speed of the stream is 5km/h

Пошаговое объяснение:

х - speed of the stream

15 + х - speed of the boat downstream

15 - x - speed of the boat contrastream

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

30(15 - x) + 30(15 + x) = 4.5(15² - x²)

450 - 30x + 450 + 30x = 1012.5 - 4.5x²

4.5 x² = 112.5

x² = 25

x = 5 (km/h)

x = -5 - impossible value