SOLUTION: A tumor is injected with 0.2 grams of Iodine-125, which has a decay rate of 1.15% per day. To the nearest day, how long will it take for half of the Iodine-125 to decay?

Question 1139498: A tumor is injected with 0.2 grams of Iodine-125, which has a decay rate of 1.15% per day. To the nearest day, how long will it take for half of the Iodine-125 to decay?
Answer by greenestamps(13203) (Show Source): You can put this solution on YOUR website!

The given information -- a decay rate of 1.15% per day -- means that each day the amount remaining at the end of the day is 100-1.15 = 98.85% of the amount at the beginning of the day. So after t days the fraction of the original amount remaining is

You want to know the number of days t it takes for the remaining amount to be half the original amount:

The variable is in the exponent, so you need to use logarithms (or a graphing calculator, or some similar mathematical aid).

to 2 decimal places.

ANSWER: to the nearest day, it will take 60 days for half of the iodine-125 to decay.
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