Posted by **Krys** on Tuesday, January 25, 2011 at 11:16pm.

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)

- Science Half Lives -
**DrBob222**, Tuesday, January 25, 2011 at 11:21pm
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 with--400 g

solve for N, the number left after time t.

k from above.

t = time = 10.8 days.

- Science Half Lives -
**Krys**, Wednesday, January 26, 2011 at 12:48am
2.7 days.. so the answer is 25 g ?

- Science Half Lives -
**kiri**, Wednesday, October 17, 2012 at 12:05pm
1. billion

- Science Half Lives -
**Amber**, Wednesday, September 24, 2014 at 12:58am
I don't know the answer to your question, but can some one help me with mine?

Question: After six half-lives, what percentage of a radioactive sample will remain?

Please help me!, Thank you.

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