Posted by Amy on .
How do I setup/solve this problem? Please help me.
The halflife of the radioactive isotope gallium70 is 20 minutes. If the initial amount of gallium70 is 25 milligrams, when will 10 milligrams be left?

math 
Reiny,
here is your same question answered.
http://www.jiskha.com/display.cgi?id=1297973911