The amount of substance that is present after t years given that the half-life of the substance is h is calculated through the equation,
A(t) = A(o)(0.5^t/h)
If after a year, the rate of decay is equal to 33.3% then,
A(t)/A(o) = (1/3) = 0.5^(1/h)
The value of h from the equation is 0.63 years.
Answer: 0.63 years