A motorboat goes 30 km upstream and 30 km back in a total of 10 hours. The speed of the stream is 4 km/h. Let the boat's still-water speed be x km/h. From 30/x-4 + 30/x+4 = 10, form a quadratic and solve by factorisation. What is the boat's speed in still water (in km/h)?

Question

Accepted Answer

8 km/h. 30/x-4 + 30/x+4 = 10 gives 30(2x) = 10(x^2 - 16), i.e. 60x = 10x^2 - 160, or x^2 - 6x - 16 = 0 = (x - 8)(x + 2). So x = 8 (reject -2). Still-water speed = 8 km/h.

A motorboat goes 30 km upstream and 30 km back in a total of 10 hours. The speed of the stream is 4 km/h.
Let the boat's still-water speed be $x$ km/h. From $\frac{30}{x - 4} + \frac{30}{x + 4} = 10$ , form a quadratic and solve by factorisation.
What is the boat's speed in still water (in km/h)?

Step-by-Step Solution

Master this chapter in 30 minutes a day.

More Class 10 Solving by Factorisation practice

A motorboat goes 30 km upstream and 30 km back in a total of 10 hours. The speed of the stream is 4 km/h.Let the boat's still-water speed be x km/h. From x−430​+x+430​=10, form a quadratic and solve by factorisation.What is the boat's speed in still water (in km/h)?

Step-by-Step Solution

Master this chapter in 30 minutes a day.

More Class 10 Solving by Factorisation practice

A motorboat goes 30 km upstream and 30 km back in a total of 10 hours. The speed of the stream is 4 km/h.
Let the boat's still-water speed be $x$ km/h. From $\frac{30}{x - 4} + \frac{30}{x + 4} = 10$ , form a quadratic and solve by factorisation.
What is the boat's speed in still water (in km/h)?