Half live of two radioactive elements A and B are 20 minutes and 40 minutes respectively. Initially, the samples have equal number of nuclei. Calculate the ratio of decayed numbers of A and B nuclei after 80 minutes.

Explanation

For radio active element A
`n_(A)=frac(80)(20)=4`
`therefore N_(A)=N_(0)(frac(1)(2))^4=frac(N_(0))(16)`
for radioactive element B
`n_(B) = frac(8)(40)=2`
`N_(B)= N_(0)(frac(1)(2))^2= frac(N_(0))(4)`
`frac(N_(A))(N_(B))=frac(frac(N_(0))(16))(frac(N_(0))(4))=frac(4)(16)=frac(1)(4)`
`thereforeN_(A) : N_(B)=1 : 4`