SOLUTION: A radioactive substance follows the decay equation dA/dt = kA. If 20% of the substance disappears in 10 years, what is its half-life?

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Question 1122744: A radioactive substance follows the decay equation dA/dt = kA.
If 20% of the substance disappears in 10 years, what is its half-life?
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!




Negative because # atoms is decreasing





Where is the quantity at time











If 20% has decayed in 10 years then the ratio of the initial amount to the ending amount is 0.80. Therefore:







So, for the half-life:



Just solve for


John

My calculator said it, I believe it, that settles it