Question 42265
Half-life is the amount of time it takes for the original amount to decay to half as much...thus in y = ae^(-0.974t), y = (1/2) a, so we have
y = ae^(-0.974t)
(1/2)a = ae^(-0.974t)
1/2 = e^(-0.974t)
take ln of both sides
ln (1/2) = -.974t
t = ln(1/2) / -.974
t = .712 days
notice that half-life is always ln(2) / k...here k was .974...