SOLUTION: Suppose the half-life of a certain radioactive isotope is 11 minutes. If 21 per cent of the initial quantity is remaining, how many minutes old is the isotope? Answer: t =

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Question 882113: Suppose the half-life of a certain radioactive isotope is 11 minutes. If 21 per cent of the initial quantity is remaining, how many minutes old is the isotope?

Answer: t = ?
Thanks so much!

Answer by josgarithmetic(39618)   (Show Source): You can put this solution on YOUR website!
Exponential Decay Equation.
A = final amount
I = initial amount
t time in minutes
k = constant for the specific decaying material

You know these values:
A=21
I=100
-
The 11 minutes half life information allows you to find k.



USE HALF LIFE TO FIND k.


------you will use this again later.

---as a formula.
The half-life data meant I=1, A=1/2, t=11.


-
Decay Equation Model,


USE DECAY EQUATION TO ANSWER t.
Start from ;
;
Substitute the known values for k, I, and A; and compute t.
A=21, I=100, k=0.06301.

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