# Math Help - urgent optimisation - finding the maximum

1. ## urgent optimisation - finding the maximum

Hi, I am stuck on part of the question:

G(t) = -0.04t^3 + 0.9t^2 + 30 predicts your grade out of 100% on the next calculus test when you study t hours during the week before the test.

I am able to differentiate but am unsure how to solve t. It doesn't fit into quadratic?

2. Originally Posted by kiwicraig31
Hi, I am stuck on part of the question:

G(t) = -0.04t^3 + 0.9t^2 + 30 predicts your grade out of 100% on the next calculus test when you study t hours during the week before the test.

I am able to differentiate but am unsure how to solve t. It doesn't fit into quadratic?
Use the first derivation:

$G'(t)=-0.12t^2+1.8t$

To get an extreme value $G'(t)=0$

Solve this equation for t. You'll get t = 0 or t = 15

Much to my surprise you'll get a grade of 30% if you don't study at all

3. thanks very much, you have really saved my bacon!