Calculus  average velocity
posted by B <3 .
*VELOCITY OF A CAR* Suppose the distance s (in feet) covered by a car moving along a straight road after t sec is given by the function s = f(t) = 2t^2 + 48t.
a. Calculate the average velocity of the car over the time intervals [20,21], [20, 20, 20.1], and [20, 20.01].
b. Calculate the (instantaneous) velocity of the car when t = 20.
c. Compare the results of part (a) with that of part (b).
*Can someone please help me? I have been trying to do my homework for some time now and I am stuck on this problem. I tried to work it out, but I did not understand what to substitute in for “t”. I used the average velocity formula and did f(t+h)f(t) divided by h …. And I got: 4t + 48. Somehow, I think this is way wrong! Can you tell me where I went wrong here and how to do this problem!?? Pleaseee!
any help would be great!!! :)

The instantaneous velocity is indeed 4t+48
However, the average velocity is the average of the instaneous velocties at two times. Example, in a, times 20,and times 20.1
v(20)=4t+48=128
v(20.1)=128.4
average: 128.2 
do you have the dike too?