Question

A person scores f(x) = 90/1 + 4e^-0.4t points on a test after t hours of studying. What does the person score without studying at all? Compute f’(0) and estimate how many points 1 hours of studying will add to the score.

Answer 1

This is what I did but my teacher said it was wrong she said ( Find f' and f'(0).)

F(x) = 90/ 1 + 4e^-0.4t
F(0) = 90/ 1 + 4e^-0.4(0) = 18
F(1) = 90/1 + 4e^-0.4(1) = 24.45
So comparing the scote at f(1) and f(0) where at f(1) studying for 1 hour and f(0) studying none.
F(1) - f(0)/24.45 – 18 = 6.45 points

Answer 2

Should this have parenteses or not?

Is this F(x) = 90/ (1 + 4e^-0.4t )?

Answer 3

yes prenthesis

Answer 4

like this \[\frac{ 9 }{ 1 + 4e ^{-0.4t}}\]

Answer 5

Your teacher specifically said to differentiate?

Answer 6

yes

Answer 7

she said to Find f' and f'(0)

Answer 8

@EulersEquation so do you know how?

Answer 9

@Numb3r1 can u help?

Answer 10

Yes. I need to review this. First glance is to use the quotient rule. Do you know how to use the quotient rule? Someone else may want to take a look. I am in the middle of helping someone else. When I finish I'll get on it.

Answer 11

ok

Answer 12

Ha! I am terrible at arithmetic. On first run I get a negative number for f'(0). You cannot make a negative score on a test! Unless the teacher doesn't like you.

I am rusty on this. I'll work on it some more. In the meantime, bump the problem and hopefully someone else will tackle this.

Answer 13

okay

Answer 14

@waterineyes

Answer 15

Just want to take derivative of that??

Answer 16

yes Find f' and f'(0)

Answer 17

It will come out to be negative..

Answer 18

what will come out? so what i did above is wrong or?

Answer 19

Wait, let we do it first..

Answer 20

\[\frac{ 90 }{ 1 + 4e ^{-0.4t}} = \frac{ -(90)(-1.6 \cdot e^{-0.4t}) }{ (1 + 4e ^{-0.4t})^2}\]

Answer 21

It will become positive now.. :)

Answer 22

okay

Answer 23

Yeah. I don't see why it has to be differentiated -- not according to the question.

Answer 24

Am I right in this?

Answer 25

Ah! I forgot to square the denominator!

Answer 26

That looks good.

Answer 27

okay thanks!

Answer 28

So you can now find f'(0) by putting 0 as value of t..

Answer 29

okay

Answer 30

@onegirl can you go for that?

Answer 31

just plug in 0 and solve right?

Answer 32

Yep, just simple calculations with calculator..

Answer 33

okay yes i can

Answer 34

Good..

Keep it up..

Answer 35

i got 0 after i solved