The half life of radium is 3.82 days. In what time will the activity decay to (1/16) of its original value.

Answer 1

1/16 = (1/2)^n
0.0625 = 0.5^n
log 0.0625 = n log 0.5
-1.20412 = n * -0.30103
n = 4 half lives
4 * 3.82 = 15.3 days