[MOVED] Half life Q: substance reduced by 30% in 20 hours

[amer88]

- Find the half-life of a radioactive substance that is reduced by 30% in 20 hours.

I need step by step procedure. Thank you very much. I appreciate all the help!

 

[stapel]

1) Use the exponential growth-decay formula they gave you: A = Pe^rt.

2) Note that, for t = 20 and P = 1 (that is, 100%), you have A = 0.7. Plug in the known values, and solve for r.

3) Plug in the known value for P and the found value for r. Note that "half-life" means "when 50% remains", and plug in the value for A. Solve for t.

If you get stuck, please reply showing how far you have gotten. Thank you.

Eliz.

 

[amer88]

1) Use the exponential growth-decay formula they gave you: A = Pe^rt.

2) Note that, for t = 20 and P = 1 (that is, 100%), you have A = 0.7. Plug in the known values, and solve for r.

3) Plug in the known value for P and the found value for r. Note that "half-life" means "when 50% remains", and plug in the value for A. Solve for t.

If you get stuck, please reply showing how far you have gotten. Thank you.

Eliz.

Thank you very much! I finally solved it and got t = 38!

I appreciate your help!