The half life of 226/88 ra is 1620 years. how much of a 220 g sample of 226/88 ra will be left after 10 half lives?

Given:
Half-life = 1620 years
Original mass, m₀ = 220 g

The decay equation is of the form

where 
t = time, years
k = constant

At half-life, m = 0.5m₀ and t = 1620. Therefore


When t = 10 half-lives = 16200 years, obtain


0.215 g (nearest thousandth)