Water coming out from a fountain is modeled by the function f(x) = -x2 + 5x + 4 where f(x) represents the height, in feet, of the water from the fountain at different times x, in seconds.

What does the average rate of change of f(x) from x = 3 to x = 5 represent?

The water falls down with an average speed of 3 feet per second from 3 seconds to 5 seconds.
The water falls down with an average speed of 5 feet per second from 3 seconds to 5 seconds.
The water travels an average distance of 3 feet from 3 seconds to 5 seconds.
The water travels an average distance of 5 feet from 3 seconds

Question

Water coming out from a fountain is modeled by the function f(x) = -x2 + 5x + 4 where f(x) represents the height, in feet, of the water from the fountain at different times x, in seconds.

What does the average rate of change of f(x) from x = 3 to x = 5 represent?

 The water falls down with an average speed of 3 feet per second from 3 seconds to 5 seconds.
 The water falls down with an average speed of 5 feet per second from 3 seconds to 5 seconds.
The water travels an average distance of 3 feet from 3 seconds to 5 seconds.
The water travels an average distance of 5 feet from 3 seconds

vocaloid · Answer

hint: 

x is the number of seconds
average rate of change = speed

vocaloid · Answer

the next step is to calculate the average speed from x = 3 to x = 5 using the formula

[f(5)-f(3)] / (5-3)

anonymous · Answer

So do i plug it in, into  f(x) = -x2 + 5x + 4 or?????

vocaloid · Answer

yes

anonymous · Answer

so I do 5-3. Which is 2 so I plug 2 into everything?

vocaloid · Answer

no, not quite...

f(5) - f(3) = ?

anonymous · Answer

f(2)

vocaloid · Answer

nope, not quite...

f(x) = -x^2 + 5x + 4 
f(5) = ?

anonymous · Answer

Im really confused?