# What is the half-life of the substance if a sample of a radioactive substance decayed to 97.5% of its original amount after a year? (b) How long would it take the sample to decay to 80% of its original amount? _______years??

##### 1 Answer

Mar 29, 2015

(a).

(b).

So:

Part (b):

So:

Taking natural logs of both sides: