# Math Help - grade 10 word problems (speed, time, distance)

1. ## grade 10 word problems (speed, time, distance)

question: An airplane has a speed of 250km/hour. One day it flies 990 kms with a tailwind, and then returns against the wind. The total trip-time is 8 hours. Find the velocity of the wind (assume it is constant).

I honestly just completely dont get this question, i dont find that the wind speed has any relevance to the question since going with and against the wind speed would just cancel itself out :S

Any help is greatly appreciated

2. ## maybe this can point u in the right direction

250km/h*8h=2000km
(2*990km)/8h=247.5km/h

But I don't get this part: "An airplane has a speed of 250km/hour."

What speed is it?

3. Originally Posted by sodapop12345
question: An airplane has a speed of 250km/hour. One day it flies 990 kms with a tailwind, and then returns against the wind. The total trip-time is 8 hours. Find the velocity of the wind (assume it is constant).

I honestly just completely dont get this question, i dont find that the wind speed has any relevance to the question since going with and against the wind speed would just cancel itself out :S

Any help is greatly appreciated
Let the wind speed by v km/hr.

With the tail wind the plane is moving at (250 + v) km/hr.
Against the wind the plane is moving at (250 - v) km/hr.

Time = distance/speed. Therefore total time of round trip is:

$8 = \frac{990}{250 + v} + \frac{990}{250 - v}$.

Solve this equation for v.

I get v = 25.