Posted by **John** on Saturday, November 25, 2006 at 2:13pm.

How many half-lives have passed if 87.5% of a substance has decomposed? How many if 99.999% has decomposed?

For 87.5% decomposition 1/8 is left.

(1/8) = (1/2)^3

Three half lives is the answer

Fot 99.999% decomposition, 10^-5 is left.

Solve 10^-5 = (1/2)^n for the number of half-lives, n. Take the log of each side of the equatiuon for a quick solution.

## Answer This Question

## Related Questions

- science - how many half-lives have passed if 87.5% of a substance has decomposed...
- Chemistry - K-42 has a half-life of 12.4 hours. If you begin with 250g of K-42, ...
- science - Using absolute dating,a fossil is dated to be 3 million years old and ...
- Science Half Lives - I am confused about how to claculate half lives. Can you ...
- chemistry - what fraction of an original sample of a radioactive isotope remains...
- half-life - 1. The half-life of a first-order reaction is 9.89 minutes. How many...
- chemistry - Find the number of disintegrations per minute emitted by 1.1 mol of...
- chemistry - how many half-lives of radon-222 have passed in 11.46 days?
- Chemistry - how many half lives have passed if only 0.625g remain of the ...
- science - how many half-lives have passed if only 1/16 of the original amount of...

More Related Questions