# Thread: Could I have some help with this maths?

2. ## Re: Could I have some help with this maths?

(a) 15 people per hr

(b). let the rate that people enter be

$r=220te^{-0.4t}+15$

use the product rule to determine the derivative of the rate, and set equal to zero to determine critical value(s) of $t$ ...

$r'(t)=220e^{-0.4t}(-0.4t +1) = 0 \implies t=2.5$

So, how would you justify $r(2.5)$ is a maximum?

3. ## Re: Could I have some help with this maths?

What happened to the original post? Did "DonkeyyourKong" erase it? That makes non-sense of skeeter's response and makes me, at least, unlikely to help "DonkeyyourKong" on any future post.

4. ## Re: Could I have some help with this maths?

well, it showed back up ...

The problem gave a rate that people enter a festival as

$\dfrac{dE}{dt}=220te^{-0.4t}+15$, $0 \le t \le 12$, where $t=0$ is noon.

part (a) asked for the rate of entrance at $t = 0$

part (b) asked for the time when the rate of entrance is a maximum.