How long will it take for 75.0% of a 0.00850 mg sample of radioactive iron-59 to decay? The half-life of iron-

Question

How long will it take for 75.0% of a 0.00850 mg sample of radioactive iron-59 to decay? The half-life of iron-59 is 45.10 days, so give your answer in days.

Answer 1

75% =1/4 . In one half live you loose 50% of radioactive material To loose 75% so 25% remaining, you must wait 2 half lives so 45.1*2 =90.2 days