Question

Selenium-83 has a half life of 25. 0 minutes. How many minutes would it take for a 10.0 mg sample to decay and have only 1.25 mg. remain?

n = ?

T = ? minutes

Answer 1

$n=n_0(\frac{1}{2})^{\frac{T}{T_{1/2}}}$

$1.25mg=10.0mg\times(\frac{1}{2})^{\frac{T}{25.0min}}$

Solving for T,

T = 75.0 minutes

Answer: 75.0 minutes