A certain radioactive element has a half-life of one hour. If you start with 20.0 grams of the element at noon, how much of the radioactive element will be left at 3 p.m.?

Question

anonymous · Answer

10.0 grams

 5.0 grams

 2.5 grams

 1.25 grams

anonymous · Answer

i do not know how to calculate these at all so if you dont mind can you show me please

anonymous · Answer

i think its 2.5

abmon98 · Answer

Mass=20 g 
Half life=1 hour
Elapsed time= 3 hour
Final amount=Intial amount/2^n
n=(elapsed time/Half life)
You are right its 2.5