# Science Half Lives

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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 -

This way.

k = 0.693/t1/2
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

solve for N, the number left after time t.
k from above.
t = time = 10.8 days.

• Science Half Lives -

2.7 days.. so the answer is 25 g ?

• Science Half Lives -

1. billion

• Science Half Lives -

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?

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