Question

Help once again please! http://nimb.ws/Wkm84q

Answer 1

@aleroth

Answer 2

a) nope

Answer 3

Okay Let me look at my work.

Answer 4

b) nope

Answer 5

Thanks @OOOPS

Answer 6

0-0"! Can you please show work so I can understand what I did wrong @OOOPS

Answer 7

hihihi.. I just use calculator to find it out
for a) when t =0, I take 120000/1250 =9.6

Answer 8

N(t) = 12 000 / ( 5 + 1245 * e^(-0.97t) )
a) N(0) = ?
b) N(5) = ?
c) N(x) = 1000 ?

Answer 9

for b) I do the same with t =5 and got the answer which is different from yours, hehehe....

Answer 10

lol oh, I was thinking in the sense that that can't 9.6 because .6 of a person can not know gossip but the whole person, but I guess it doesn't matter with math.

Answer 11

@aleroth a= 9.6 b=735.746 c=I don't know >-<

Answer 12

So a) 9.6 being rounded to 9 people makes sense.
b) I get 813?

Answer 13

0o0"! How?!

Answer 14

@aleroth

Answer 15

12 000 / ( 5 + 1245 * e^(-0.97*5) ) =
12 000 / ( 5 + 9.74 ) =
12 000 / 14.74 = 814

Answer 16

Oh, okay I don't know what the heck I did to get that answer >_< Thanks ^^. Can You help with c @aleroth ?

Answer 17

c resembles the other exercise a lot, show me how far you can get without help :D

Answer 18

You just want to get the equation to equal 1000, by getting t alone

Answer 19

I know :) but this division bar is scaring me . 1000=12,000/(5+1245e^(-0.97t)

Answer 20

I subtracted 12,000 from each side.

Answer 21

brb

Answer 22

Alright, subtracting 12000 from both sides won't do what you think it does. When a number is multiplied or divided by something, then simply subtracting/adding won't get rid of it.

See here for example:
2/x = 4
2/x - 2 = 4 - 2 <-- This thing is not the same thing as 0/x = 2??

Answer 23

Oh okay. I would like to be honest with you and say that example confuses me...

Answer 24

Okay, so you want to get the variable t all by itself. So it can't be in a denominator, it has to be on top, like t/1 is the same thing as t.

Answer 25

Yes :) that is true.

Answer 26

Right, so the trick to getting it up there is multiplying both sides by that denominator. you see?

Answer 27

Oh okay.

Answer 28

Now when you do that, the whole denominator will get over on the left side and on the right side you have the same thing in both the numerator and the denominator, so they cancel out and become 1, which you don't even need to write.

Answer 29

Okay.

Answer 30

You see it??

Answer 31

Yes, sorta, it's still some foggy spot but I see where your going with the concept.

Answer 32

You get:
(1000)(5+1245e^-0.97t) = (12000)/(5+1245e^-0.97t)*(5+1245e^-0.97t)

See how on the right side you get (5+1245e^-0.97t) in the denominator and numerator, which cancel and become 1.

So you simplify the whole thing to:
(1000)(5+1245e^-0.97t) = (12000)

Answer 33

This trick is really important to learn for further math (getting stuff up from the denominator)

Answer 34

Do you see how it works out?

Answer 35

Oh okay ! Thank you. And yes I see!

Answer 36

Awesome, do you know how to solve this from here or should I continue?

Answer 37

You should continue so I can see how it's done the total right way.

Answer 38

(1000)(5+1245e^-0.97t) = (12000)

You are working towards getting t all by itself.
So let's get rid of the thousand. We can't subtract by 1000, because it is multiplied by something else. You have to divide by 1000, yes!

(1000)(5+1245e^-0.97t)/1000 = (12000)/1000
Simplifies to:
(5+1245e^-0.97t) = (12)

Here we can subtract the 5 from both because it is NOT multiplied by something else!
1245e^0.97t = (12) - (5)

Answer 39

(I missed a minus sign in the line above!)
1245e^-0.97t = 7

1245e^-0.97t = 7 is just another way to write 1245*e^(-0.97*t) = 7

Now we see we can divide by 1245, so you get:
e^(-0.97*t) = 7/1245

Now we use logarithm again:
ln(e^(-0.97*t) = ln(7/1245)

-0.97*t = ln(7/1245)

Now we divide both sides, by -0.97 (note can't subtract!):
t = ln(7/1245)/(-0.97)

Answer 40

Calculating that should give you the answer.

This was a lot of writing for one exercise, but I hope you learned something..

Answer 41

Yes I am very grateful and amazed by your brilliance. I really do I appreciate it :)

Answer 42

And I learned a new trick. Thank you! :)