# A radioactive substance has a half-life of 125 years - if there were originally 80 radioactive milligrams 50 years ago, how much is still radioactive today?

##### 1 Answer

May 13, 2018

#### Explanation:

Radioactive decay constant (

#λ = "ln(2)"/("T"_"1/2") = "ln(2)"/"125 years"#

Amount of radioactive substance left after time

#"N = N"_0 e^-(λt)#