Question

A hiker in Africa discovers a skull that contains 72% of it's original amount of c-14.
N=Noe^-kt
No=initial amount of C-14(at time t=0)
N=amount of C-14 at time t
t=time, in years
k=0.0001

Find the age of the skull to the nearest year.

Answer 1

shouldnt it just be plug and play? plug into eq'n?

Answer 2

Im... not sure. Honestly.

Answer 3

I have no idea how to do this stuff, at all.

Answer 4

sorry. went to do stuff.

Answer 5

It's fine, I'm the beggar here anyways.

Answer 6

There's no otehr eq'n?

Answer 7

I took a closer look and realized I'm stumped too. I use to remember exactly how to solve this problem.

Answer 8

I think its a 2 step problem.

Answer 9

I'm completely stumped on this.
No idea what to do.

Answer 10

First we look for the initial amt.

Answer 11

u have one equation u need to solve that equation for (t)

Answer 12

N = .72

Answer 13

is that so? I don't think we can put % there. but then again, its been a while

Answer 14

e's an actual numerical value, last i remember.

Answer 15

you got a scientific calculator?

Answer 16

mhm

Answer 17

Its like the opposite of In (pronounced lawn)

Answer 18

that's confusing xD

Answer 19

do you see it on your calculator?

Answer 20

\[e ^{x}\]

Answer 21

yes

Answer 22

anyways, if we go back to solving the initial amount, N=No, k=0.0001, t=0.

Answer 23

wait...that doesn't help at all...

Answer 24

It helps to restate a bit

Answer 25

We're looking to find the time

Answer 26

i understand that much. Just trying to find the other variables first...

Answer 27

that seems to be impossible for me

Answer 28

What if you subbed in:
No=1
N=0.72
t=?
k=0.0001

Answer 29

And then rearranged to solve for t?

Answer 30

I was thinking of trying that.

Answer 31

How does No = 1, just for ed purposes?

Answer 32

1 is just 100% compared to 0.72.

Answer 33

What's the opposite of e^x? Is it called negative reciprocal?

Answer 34

In

Answer 35

aka, -inf

Answer 36

I guess that's what you use on both sides to get rid of that e^x.

Answer 37

Is the answer in your textbook?

Answer 38

No :(

Answer 39

darn.

Answer 40

Well, have you tried anything else here?

Answer 41

nooooo, that's wrong!!! I'm African and this bullcrap doesn't happen.

Answer 42

hey, same here.

Answer 43

you got anything, ralph?

Answer 44

Well, I'm out. Sorry.

Answer 45

I got this.

Answer 46

N=Noe^-kt
No=initial amount of C-14(at time t=0)
N=amount of C-14 at time t
t=time, in years
k=0.0001
You know that N=0.72 No. Substitute that in, and divide by No on both sides to get 0.72=e^-kt. Then, take the natural log of 0.72, multiply by 10,000 (to account for k) and you have t.

Answer 47

Just so I understand, how do you take natural logs?

Answer 48

me, I didn't try, but I think it's easy.

Answer 49

It looked easy to me too.

Answer 50

Guess its really has been a while.

Answer 51

It's a button on any decent calculator, including Google Calculator.

Answer 52

the OP is probably already asleep. Good job trying though.

Answer 53

you just pres the log button?

Answer 54

ay.

Answer 55

No. That's usually log base 10, you need log base e.

Answer 56

so... (log)+(e^x)?

Answer 57

NO.

Answer 58

lol

Answer 59

Sorry. If you only have the log button and not the ln button you can take \[\log_{10} x \div \log_{10} e\]