Rather than use that formula, look at the attachment and use the 4th equation.
Ending Amount = Beginning Amount / 2^n
where "n" is the number of half-lives. "n" = elapsed time / half-life
(Is 934 the beginning amount? Let's say it is.)
for 40 years, n=40/30 = 1.3333333...
Ending Amount = 934 / 2^1.3333333...
Ending Amount = 934 / <span> <span> <span> 2.5198420998 </span> </span> </span>
Ending Amount = <span> <span> <span> 370.66 grams
</span></span></span>
for 100 years, n=100/30 = <span> <span> <span> 3.333333 </span> </span> </span> ...
Ending Amount = 934 / 2^<span> <span> 3.333333 </span> </span> ...
Ending Amount = 934 / <span> <span> <span> 10.0793683992 </span> </span> </span>
Ending Amount = <span> <span> <span> 92.66 grams
Source:
http://www.1728.org/halflife.htm
</span></span></span>
Ending Amount = Beginning Amount / 2^n
where "n" is the number of half-lives. "n" = elapsed time / half-life
(Is 934 the beginning amount? Let's say it is.)
for 40 years, n=40/30 = 1.3333333...
Ending Amount = 934 / 2^1.3333333...
Ending Amount = 934 / <span> <span> <span> 2.5198420998 </span> </span> </span>
Ending Amount = <span> <span> <span> 370.66 grams
</span></span></span>
for 100 years, n=100/30 = <span> <span> <span> 3.333333 </span> </span> </span> ...
Ending Amount = 934 / 2^<span> <span> 3.333333 </span> </span> ...
Ending Amount = 934 / <span> <span> <span> 10.0793683992 </span> </span> </span>
Ending Amount = <span> <span> <span> 92.66 grams
Source:
http://www.1728.org/halflife.htm
</span></span></span>