# Math Help - Radioactive Decay...Part 2

Iodine 131 is a radioactive material that decays according to the function A(t) = A_0(e)^(-0.087t) where A_0 is the initial amount present and A is the amount present at time t (in days). Assume that a scientist has a sample of 100 grams of iodine 131.

Note: A_0 is read: "A sub zero"

(c) When will 70 grams of iodine 131 be left?

(d) What is the half-life of iodine 131?

2. part a: $70=100e^{-.087t}$, solve for t.

Half life can be gotten from $T=\frac{-1}{k}ln(2)$

What does upper case T and lower case k stand for in your half-life formula?

4. k is the decay constant.

T is the half life time.

So, your half life would be $\frac{-1}{-.087}ln(2)\approx 7.97$

5. ## But...

But I want to know what numbers do I replace k and T with in the half-life formula you shared.

Thanks