SOLUTION: Radioactive element R decays exponentially at a rate of 4% per year. If we begin with 5 grams of R, how long (to the nearest tenth of a year) will it take for only 3 grams to remai

SOLUTION: Radioactive element R decays exponentially at a rate of 4% per year. If we begin with 5 grams of R, how long (to the nearest tenth of a year) will it take for only 3 grams to remai

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Question 240608: Radioactive element R decays exponentially at a rate of 4% per year. If we begin with 5 grams of R, how long (to the nearest tenth of a year) will it take for only 3 grams to remain?
I started with the A=Aoe^rt where A=3 Ao=5 r=0.04 and t is what I needed to find. I then to ln3=ln5+0.04tlne. Then I got the 0.04t=(ln3-ln5)/lne....
Answer by scott8148(6628) (Show Source): You can put this solution on YOUR website!
3 = 5 e^(-.04t)

.6 = e^(-.04t)

ln(.6) / -.04 = t

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