Posted by **Roger** on Tuesday, September 20, 2011 at 8:43am.

Suppose the function G(t) represents a test grade (out of 100 points) as a function of hours studied. If

G(t)=-0.046t^3+0.915t^2+38.005 points, what is (dG/dt)when t=4? Round your answer to the nearest point per hour.

a. 50 points per hour

b. 3 points per hour

c. 5 points per hour

d. 7 points per hour

e. 20 points per hour

- calculus -
**Writeacher**, Tuesday, September 20, 2011 at 8:48am
Your umpteen posts have been removed.

Once you write up **WHAT YOU THINK**, please re-post, and someone here will be happy to comment.

- calculus -
**Roger**, Tuesday, September 20, 2011 at 8:52am
WHY ARE YOU DELETING MY POSTS?

- calculus -
**Writeacher**, Tuesday, September 20, 2011 at 9:00am
To quote one of our very good math and science tutors: **"You will find here at Jiskha that long series of questions, posted with no evidence of effort or thought by the person posting, will not be answered. We will gladly respond to your future questions in which **__your thoughts__ are included."

- calculus -
**Anonymous**, Tuesday, September 20, 2011 at 9:14am
Derivative of t ^ 3 = 3 * t ^ 2

Derivative of t ^ 2 = 2 * t

Derivative of 38.005 = 0

dG / dt = - 0.046 * 3 * t ^ 2 + 0.915 * 2 t + 0 = - 0.138 * t ^ 2 + 1.83 * t

When t = 4

then :

dG / dt = - 0.138 * 4 ^ 2 + 1.83 * 4

dG / dt = - 0.138 * 16 + 7 . 32

dG / dt = - 2.208 + 7.32

dG / dt = 5.112

Rounded to the nearest point per hour :

dG / dt = 5 points per hour

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