Question

sodium-25 was to be used in an experiment but it took 3.0 minutes to get the sodium from the reactor to the laboratory if 5.0 mg of sodium-25 was removed from the reactor how many mg of sodium-25 were placed in the reaction vessel 3.0 minutes later if the half-life of sodium-25 is 60 seconds

Answer 1

3 half lives later... 5/2 = 2.5mg, then 2.5/2 = 1.25 mg, then 1.25/2 = .625 mg left