A radioactive isotope decays exponentially at a rate of 0.0111% each year.
How long will it take 500 g of the isotope to decay to 150 g? Round your answer to the nearest whole
number.
I got 120 but it says that it is wrong, can someone explain this problem to me?

you need to add a picture

7 is the median   7.875 is the mean

step-by-step explanation:

3,4,5,6,8,11,13,13

combine all like terms then its just a 2 step equation

ending amount = beginning amount / (2^n)

where "n" = number of half-lives (or elapsed time / half-life)

ending amount = 50 mg / (2 ^10 / 5.3)

ending amount = 50 mg / (2 ^ 1.8867924528)

ending amount = 50 m / 3.6981210597

ending amount = 13.5203794557 mg

or about 13.5 mg remain

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