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a 500 mg known substance in fossils decays at a rate of 10% per year. scientists find a fossil with 295.25 mg of the known substance. how old is the fossil?

x ≈ 5 years

Step-by-step explanation:

Given amount = A = 500 mg

Decay rate = r = 10% per year

Remaining amount = L = 295.25 mg

The formula to calculate remaining amount after x years decay =

L = A((100-r)/100)^x

By putting values in this formula, we get

295.25 = 500 ((100-10)/10)^x

295.25 = 500 (0.90)^x    

295.25/500 = 0.90^x

0.5905 = 0.90^x

0.90^x =0.5905

taking log on both sides

ln(0.90^x) =ln(0.5905)

x*ln(0.90) =ln(0.5905)  using property of log

x = ln(0.5905)/ln(0.90)

x = 4.9984

x ≈ 5 years