If 250 mg of a radioactive element decays to 200 mg in 12 hours, find the half-life of the element. (Round your answer to the nearest whole number.)
200 = 250 x 1/2^(12/t), where t=half-life
0.8 = 1/2^(12/t) Take the natural log of both sides
-0.22314355 =(12/t) x -0.69314718 Cross multiply
-0.22314355 t =-8.317766 Divide both sides by -0.22314355
t = 37.275 =~37 hours - the half-life of this material.
We have that
200 = 250(.5)^(12/h) where h is the half-life in hours
Divide both sides by 250
200/250 = (.5)^(12/h)
.8 = (.5)^(t/h) take the log of both sides
log (.8) = log(.5)^(12/h)
And by a log property we can write
log (.8) = (12/h) log (.5)
Rearrange to isolate h
h = 12log(.5) / log(.8) ≈ 37.28 hrs