Analyzing Rational Functions

Question

Lenny Leonardson can paddle in still water at a speed of 4km/h. If he paddled 8km upstream against the current and then paddled 8km back downstream with the current and the total trip took 5h, what is the speed of the current?

The answer is 1.79 km/h

Answer 1

This is what we like to call in algebra "Dirt" problems, or distance = rate x time. (drt)

Time is constant for both the train and the car. Let x = the average speed of the car, so we first need to solve for time and then set both the equations together.

t = distance/rate.

450/x = 350/(x-20) --> the car distance divided by the car speed equals the train distance divided by the train speed which is 20 km/h slower than the car's speed.

Dividing both sides by 450 and multiply by x-20:

(x-20)/x = 350/450

1 - 20/x = 7/9

Multiply both sides by x

x-20 = 7x/9

2x/9 = 20

x = (9/2)20 = 180/2 = 90 km/h