SOLUTION: (Only a four function calculator can be used) Radioactive isotope of Iodine is used in many hospitals in medical diagnosis. The isotope decays exponentially over time. The clini

Question 934634: (Only a four function calculator can be used)
Radioactive isotope of Iodine is used in many hospitals in medical diagnosis. The isotope decays exponentially over time. The clinic received a shipment of this isotope on 1-16-15. On 1-19-15 there were 100 unites remaining and today 1-21-15, 918 units remain.
a. Write an equation for the relationship between units of isotope and time.
b. How much of the isotope will be left 10 days from today in none used?
c. How long will it take for the number of units to fall below 100 if none is used?
Answer by josgarithmetic(39625) (Show Source): You can put this solution on YOUR website!
The form for your model is . Exponential decay.
I, initial amount
A, amount after time t days
The amount of the shipment received on 1-16-2015 in unknown, and might not be needed.

The description includes that 100 grams became 918 grams in a two day period.
Use that to find the value for k.
-

-
The value for k evaluated into a decimal form,

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That is not working, and after rechecking your question description, something is very wrong:
On 1-19-2015, the amount of the isotope was 100 units.
On 1-21-2015, just TWO days later, the amount was 918 units.
That cannot be. The isotope DECAYS, so as time progresses the amount remaining must DECREASE!

Fix your question and problem description. My steps may help anyhow.
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