The half life of iodine-125 is 60 days. What was the initial amount of iodine-125 if you have 4.5 grams after 360 days?

288 grams

Explanation:

The amount of any radiative substance left after some time is calculated by

amount left =

where x is the initial amount of substance

n is the number of half lives

one half live is the time in which amount of substance reduce to half of its initial value.

------------------------------------------------------

amount left = 4.5 grams

half life of  iodine-125 = 60 days

total time in which substance reduced to 4.5 grams  = 360 days

thus,

number of half life in 60 days = 360/60 = 6

thus, there are period of 6 half lives

in each half life the amount of substance reduces to its previous half

let the initial amount be x grams

using the formula

amount left =

Thus, 288 grams was the initial amount of iodine-125