# Chemistry

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.

1. 👍 0
2. 👎 0
3. 👁 338

## Similar Questions

1. ### science

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

asked by Kim on March 14, 2011
2. ### math

The half life of the radio active substance is the time require the half the substance to decay. the mount A ( in grams) of 100 gram sample of a radio active substance remaining after t half lives by A equals to 100 (0.5) t.

asked by sai on January 17, 2018
3. ### science

Using absolute dating,a fossil is dated to be 3 million years old and decomposed 1 half-life. If it takes the same fossil 12 million years to decompose to 4 half-lives,how old will the fossil be when it is measured to be at

asked by Cherie on May 25, 2012
4. ### Science

If the initial amount of Carbon-14 in the mammoth was 8 grams, how many half-lives have passed i the fossil sample has 1 gram left? How many years have passed since the mammoth's death?

asked by Anonymous on November 2, 2017
5. ### chemistry

how many half-lives of radon-222 have passed in 11.46 days?

asked by Jerry on May 23, 2011
6. ### algebra

1) how many billions of years will it take 1000 grams of uranium-238 to decay to just 125 grams? 2) a researcher had 37.5 g left from a 600 g sample of sulfer-35. how many half-lives passed during that time? 3) look at problem 2.

asked by anon on May 9, 2013
7. ### Chemistry

how many half lives have passed if only 0.625g remain of the original 40g?

asked by Sally on January 28, 2013
8. ### science

how many half-lives have passed if only 1/16 of the original amount of the element remains? a-two b-three c-four d-five

asked by Anonymous on September 28, 2011
9. ### chemistry

what fraction of an original sample of a radioactive isotope remains after three half-lives have passed? 1/8?

asked by jake on October 13, 2012
10. ### Calculus

Write the recurring decimal 0.abcabcabcâ€¦ as a fraction. a) (a+b+c)/999 b) (100a+10b+c)/999 c) (abc)/999 --> I did this but my teacher said I was wrong d) (100c+10b+a)/999

asked by Alice on April 11, 2019

More Similar Questions