A tumor is injected with 0.5 grams of Iodine-125, which has a decay rate of 1.15% per day.

Question

Write an exponential model representing the number of grams f of Iodine-125 remaining in the tumor after t days

f(t)=?

I already tried 0.5e^-0.0115t

Then use the formula to find the amount of Iodine-125 that would remain in the tumor after 60 days. (Round your answer to four decimal places.)

Answer 1

The formula for exponential decay is f(t)=ae^kt where a is the original amount of the substance, k is the decay rate and t is the time elapsed. You are given the decay rate of 1.15% or -0.0115. For this problem t is left as is since we are creating a function of time. So, your model is indeed f(t)=0.5e^-0.0115t. It is important to note that care should be taken when writing a. Problems may want you to put it in terms of other units such as kilograms, in which case a=0.0005.

If you are writing this formula into an online program, check to see the format required to submit. For example, instead of f(t) try f.

For the second part, you will use t=60. You shouldn't need to convert the time.