After 75 minutes, a sample of 280 grams of radioactive goo has decayed to 17.5 grams. The half-life of the radioactive is 18.75 minutes.
The problem can be solved using decay model. The formula of decay system is given by:
Nt = No . e^(-λ . t)
Where:
Nt = quantity at time t
No = initial quantity
λ = decay constant = ln(2) / T
T = half life
The above formula can be rearranged to:
T = t . ln(2) / [ln(No/Nt)]
Parameters given in th problem:
No = 280 grams
t = 75 minutes
Nt = 17.5 grams
Plug these parameters into the formula:
T = 75 . ln(2) / [ln(280/17.5)]
= 18.75 minutes
Hence, the half-life of the radioactive goo is 18.75 minutes.
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