problem.. I've been given this question as my homework over the holiday, and I've come to attempt it and I'm completely stumped, as are most in my class so could you guys point me in the right direction? question.. Uranium decays into lead. The half life of uranium is 4,000,000,000 years. A sample of radioactive rock contains 7 times as much lead as it does uranium. Calculate the age of the sample. my guess.. Just thinking over as I write it, would I have to see how long it would take the uranium to decay completely then divide it by 7?