Question

The half-life of cobalt-60 is 5 years. How old is a sample of cobalt-60 if only one-eighth of the original sample is still cobalt-60?.

Answer 1

`\tt \large{\boxed{\bold{Nt=No.((1)/(2)) ^{(T)/(t1/2) } }}`

Nt/No = 1/8

T = duration of decay

t 1/2 = half-life

`\tt (1)/(8)=(1)/(2)^(T)/(5)}\\\\((1)/(2))^3=(1)/(2)^(T)/(5)}\\\\3=(T)/(5)\rightarrow T=15~years`