Question

A wildlife photographer photographs a crocodile and then paddles against a river current for 6 km. Then, hoping to photograph a hippopotamus, she paddles 15 km across a lake. She paddles across the lake for one hour longer than she paddled up the river. Find the speed of the boat as she paddles if the river current is 2 km/h (2 answers)

Answer 1

Explanation:

5 km/h or 6 km/h

Explanation:

Let the speed of the boat be x

Speed against the current in the river is x - 2

Time in the river:

6/(x - 2)

Time in the lake:

15/x

The difference:

6/(x - 2) = 15/x - 1

Solve for x to find the speed of the boat

Multiply both sides by x(x - 2) to clear the fraction:

6x = 15(x - 2) - x(x - 2)

6x = 15x - 30 - x² + 2x

x² - 11x + 30 = 0

(x - 5)(x - 6) =0

x -5 = 0, x - 6 = 0

x = 5 km/h, x = 6 km/h