Question- A) You is using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the reading of 400. Counts has diminished to 100. Counts after 62.6 minutes what is the half-life of this substance?
B) An unknown radioactive substance has a half-life of 3.20 hours. If 41.9g of the substance is currently present, what mass A0 was present 8.00 hours ago?
C) Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 45.0% of an Am-241 sample to decay?
D) A fossil was analyzed and determined to have a carbon-14 level that is 20% that of living organisms. The half-life of C-14 is 5730 years. How old is the fossil?
Here is the problem which I am struggling on, please help me