Question 1129845
The half-life of element X is 13.25 minutes,
 if the original of the sample is 2.36 kg,
 how long will it take in HOURS for the remaining mass to be 12.0 grams ?
:
The radio active decay formula
A = Ao*2^(-t/h) where
A = remaining amt after t time
Ao = initial amt
t = time of decay
h = half-life of substance 
:
Change 2.36 kg to 2360 grams
2360*2^(-t/13.25} = 12
2^(-t/13.25) = {{{12/2360}}}
{{{ln(2^(-t/13.25))}}} = {{{ln(12/2360)}}}
the log equiv of exponents
{{{-t/13.25}}}ln(2) = {{{ln(12/2360)}}}
{{{-t/13.25}}} = {{{ln(12/2360)/ln(2)}}}
Using our calc
{{{-t/13.25}}} = -7.61961
t = -13.25 * -7.61961
t = 100.9598 ~ 101 minutes
which is
101/60 = 1.68 hrs