Question

radium-226 has a half life of about 400 years . after 600 years how much radium would be left if you started with 1000 mg?

Answer 1

find an exponential decay equation for the amount left

Answer 2

do you know how to do this?

Answer 3

no

Answer 4

Ending Amount = Beginning Amount / 2^n
where 'n' is equal to elapsed time / half-life

Answer 5

The half life of radium 226 is 1,601 years
https://en.wikipedia.org/wiki/Radium

Answer 6

1,000 mg after 600 years ?
Ending Amount = Beginning Amount / 2^n
where 'n' is equal to elapsed time / half-life

'n' = 600/1,601
Ending Amount = 1,000 mg / 2^(0.374765771392879)
Ending Amount = 1,000 mg / 1.29662902348742
Ending Amount = 771.23 mg

Assuming you had to determine this for substance 'x' which has a half-life of 400 years:
Ending Amount = Beginning Amount / 2^n
'n' = 600/400 = 1.5
Ending Amount = 1,000 mg / 2^1.5
Ending Amount = 1,000 mg / 2.82843
Ending Amount = 353.55339 mg