91Ó°ÊÓ

Within two years of publication, $13\%$ of the internet sites cited in major scientific publications vanish.

Multiplication rule: $P(Aâˆ\copyright B)=P\left(A\right)×P\left(B\right)$

Complement rule: $P(notA)=1−P\left(A\right)$

$P\left(lost\right)=13\%=0.013$

Complement rule:

$P(notA)=1−P\left(A\right)$

Calculate the likelihood of a reference not being lost within two years using the complement rule.$P(notlost)=1−P\left(lost\right)=1−0.13=0.87$

Multiplication rule:$P(Aâˆ\copyright B)=P\left(A\right)×P\left(B\right)$

To find the likelihood of not losing within $7$references, use the multiplication rule:

$P(7notlost)={(P(notlost\left)\right)}^7={(0.87)}^7≈0.3773$

To calculate the probability of getting at least one losing within two years, use the complement rule:

$$\begin{gathered} P(atleastonelost)=1−P(7notlost) \\ P(atleastonelost)=1−0.3773 \\ P(atleastonelost)=0.6227 \\ P(atleastonelost)=62.27\% \end{gathered}$$