Here is the question:
An unknown radioactive element decays into non-radioactive substances. In days the radioactivity of a sample decreases by percent.
(a) What is the half-life of the element?
(b)How long will it take for a sample of mg to decay to mg?
I've tried it several times and I keep getting the same answers which are wrong
I used I integrate this and got .
I used which gave me the equation .
I then plugged in for y and 400 for t from the question. this gave me k= 0.0025. giving me the equation .
I then set and solved for t to get the half life. Which gave me the answer 277 days.
What am I doing wrong?