6. After 24.0 days, 2.00 miligrams of an original 128.0 milligram sample remain. What is the half-life of the sample? [!]
   4.00 days
7. How long will it take for a 40.0 gram sample of I-131 (half life = 8.040 days) to decay to 1/64 its original mass?
   6*8.040 = 48.24
8. Fermium-253 has a half-life of 0.334 seconds. A radioactive sample is considered to be compltely decayed after 10 half-lives. How much time will elapse for this sample to be considered gone?
   0.334*10 = 3.34
9. At time xero, there are 10.0 grams of W-187. If the half-life is 24.0 hours, how much will be present at the end of one day? Two days? Seven days?
   5, 2.5, 0.7
10. 160.0 grams of an isotope with a half-life of 36.0 hours is present at time zero. How much time will have elapsed when 5.00 grams remains?
    6 half-lifes
11. How much time will be required for a sample of H-33 to lose 75% of its radioactivity? The half-life fof tritium is 12.26 years.
    26*2 = 24.52