Question

The speed of the current in a river is 6 mph. A ferry operator who works that part of the river is looking to

Answer 1

Answer:

• 9 mph

Step-by-step explanation:

Let he speed of the boat on the lake is x.

Considering the speed of the current it will take him:

• 22.5/(x + 6) + 22.5/(x - 6) = 9
• 2.5 / (x  + 6) + 2.5 / (x - 6) = 1
• 2.5(x - 6 + x + 6) = (x + 6)(x - 6)
• 2.5*2x = x² - 36
• x² - 5x - 36 = 0
• x = (5 ± √(5² + 4*36))/2 = (5 ± 13) / 2
• x = (5 + 13)/2 = 9 mph (negative root is discarded as the speed should be positive)