tertie said:
Can I ask for assistance one more time?
A plane flies at 720 mi against a steady 30-mi/h headwind and returns to the same point with the wind. If the entire trip takes 10 h, what is the plane's speed in still air?
now I know that d=r(t)
x=720(10) = 7200
now do I divide by 30? (=240) than add that to the 720??
You've already received one suggestion as to how to set up the problem. I'll offer a slightly different approach.
Let r = speed of plane in still air
Flying
against the wind, the plane's speed will be reduced by the wind speed, and its rate will be r - 30 mph. We know that distance = rate * time, and that distance/rate = time. So,
time flying against the wind = 720/(r - 30)
Flying
with the wind, the plane's speed will be increased by the wind speed, and its rate will be r + 30 mph. So,
time flying with the wind = 720/(r + 30)
We also know this: the total time for the trip was 10 hours. Thus,
time against wind + time with wind = 10
Code:
720 720
------ + ------- = 10
r - 30 r + 30
Now, you should be able to solve for r. Hint: multiply
both sides of the equation by the common denominator for the fractions.
I hope this helps you.