Science Half Lives
posted by Krys .
I am confused about how to claculate half lives. Can you explain. ( How much of a 400 gm sample od gold is left after 10.8 days if the half life is 2.7)

This way.
k = 0.693/t_{1/2}
You don't have any units for the half life of 2.7 WHAT? Make sure unit for this agrees with unit below (in days).
Substitute k into the equation below.
ln(No/N) = kt
No = what you start with400 g
solve for N, the number left after time t.
k from above.
t = time = 10.8 days. 
2.7 days.. so the answer is 25 g ?

1. billion

I don't know the answer to your question, but can some one help me with mine?
Question: After six halflives, what percentage of a radioactive sample will remain?
Please help me!, Thank you.