Math
posted by Jayson .
An airplane has a speed of 400 km/h with no wind. The airplane flies 2140 km with the wind. The airplane can only fly 1860 km against the wind in the same time. If w equals the speed of the wind, which equation would be used to find w?
a) 2140/(w+400) = 1860/(w400)
b. 2140/(400+w)  1860/(w400)=21401860/w
c) 2140/(400+w) = 1860/(400w)
d) 2140/(400+w)  1860/(400w) = 650
2. What is the average rate of change of f(x)= (x5)/(x+3) from x=2 to x =4?
a) 24/7
b) 8/7
C) 25/21
D) 11/3
Can someone explain to me what to do with the denominators? that's the only thing I am confused about. I know that you plug in 2 for x, f(x)= (x5)/(x+3)
Y2Y1/X2X1

anyone?? D:

I assume you got C for #1.
Time = distance/speed
The two times are equal
#2.
f(2) = 7/1
f(4) = 1/7
So, over an interval of 6 units, y changed from 7 to 1/7 = +48/7
So, the average change per unit is (48/7)/6 = 8/7 
How did you get the denominator 1 and 7? That is what I am confused :3

You're kidding, right?
f(x)= (x5)/(x+3)
f(2) = (25)/(2+3) = 7/1
f(4) = (45)/(4+3) = 1/7