Posted by **Dee** on Sunday, November 17, 2013 at 4:10pm.

An isotope of lead, 201Pb, has a half-life of 8.4 hours. How many hours ago was there 40% more of the substance? (Round your answer to one decimal place.)

____hr

- college algebra -
**Steve**, Sunday, November 17, 2013 at 4:14pm
If there was 40% more, then that's 1.4 times what's there now.

So, starting with an original amount of 1, there is now 1/1.4 of it left.

(1/2)^(t/8.4) = 1/1.4

Now just solve for t hours.

Note: It will be less than 8.4, since 8.4 hours ago, there was 100% more.

- college algebra -
**Dee**, Monday, November 18, 2013 at 9:24pm
not sure how to find the t, tried using the log approach but can't get the right answer.

## Answer this Question

## Related Questions

- college algebra - Use a calculator to help solve the problem. An isotope of lead...
- College Algebra - Use a calculator to help solve the problem. One isotope of ...
- college algebra - In 4 years, 30% of a radioactive element decays. Find its half...
- college algebra - One isotope of holmium, 162Ho, has a half life of 22 minutes. ...
- Half-life - After two hours, 1/16 of the initial amount of a radioactive isotope...
- linear/exponential - This question involves the half-life formula. In this ...
- chm - An unknown radioactive substance has a half-life of 3.20 . If 34.8 of the ...
- Calculus Help Please!!! - A radioactive substance has a half-life of 4 days. ...
- Chemistry Help Please!!! - A radioactive substance has a half-life of 4 days. ...
- Math. Have answer, please show work - In a tracer method the potassium isotope ...

More Related Questions