The radioactive isotope of lead, Pb-209, decays at a rate

Last updated: 7/10/2022

The radioactive isotope of lead, Pb-209, decays at a rate proportional to the amount present at time t and has a half-life of 3.3 hours. If 1 gram of this isotope is present initially, how long will it take for 85% of the lead to decay? (Round your answer to two decimal places.) hr