If the half-life of 1-131 is 8.2 days, how long would it take for 1-131 to go through 3 half-lives?

Given specimens uranium-232 (t1/2=68.9y) and uranium-233 (t1/2=159,200y) of equal mass, which one would have greater activity and why?

Given specimens neon-24 (t1/2=3.38min) and bismuth-211 (t1/2=2.14min) of equal mass, which one would have greater activity and why?

A sample of rock was found to contain 8.23 mg of rubidium-87 and 0.47 mg of strontium-87.. (a) Calculate the age of the rock if the half-life of the decay of rubidium by emission is 4.71010 y. (b) If some S3887r was initially present in the rock, would the rock be younger, older, or the same age as the age calculated in (a)? Explain your answer.