+6 a radioactive element has a half-life of 1.1 billion years. A rock contains 6.25% Parent material. How old is the rock.
+37146 How many half lives to get to 6.25%
100%
1 50%
2 25%
3 12.5%
4 6.25% 4 half lives
Another way 1/2^n = .0625
Take the log of both side
n log 1/2 = log .0625
n = log (.0625 ) / log (1/2) = 4 half lives
4 half lives x 1.1 billion yrs/halflife = 4.4 billion years old
