Question

The half-life of radium is about 1760 years. In how many years will one gram of radium decay to .95 g

Answer 1

Ending Amount = Beginning Amount / 2^n
where "n" is the number of half-lives (time / half-life)
Ending Amount = 1.0 / 2^n
2^n = 1.0 / .95
2^(time / half-life) = 1.0526315789

elapsed time = half-life* (log (bgng amt / end amt) / log(2)
elapsed time = 1,760 * log (1.0526315789) / 0.30102999566
elapsed time = 1,760 * 0.022276394692 / 0.30102999566
elapsed time = 130.2410232308 years