If 15% of the radioactive material decays in 5 days, what would be the percentage of amount of original material left after 25 days?

Answer 1

ln(No/N) = kt
No = 100
N = 85
t = 5 days
solve for k

Then
ln(No/N) = kt
No = 100
N = ? solve for this amount remaining.
k = from above
t = 25 days

N is what is left. (N/100)*100 = % remaining

Answer 2

n(No/N) = kt
No = 100
N = 85
t = 5 days
solve for k

Then
ln(No/N) = kt
No = 100
N = ? solve for this amount remaining.
k = from above
t = 25 days

N is what is left. (N/100)*100 = % left

Answer 3

how the N becomes 85 in first ?

Answer 4

No clarity