bac-s-maths 2018 Q1A

bac-s-maths · France · polynesie Tree Diagrams Total Probability Calculation
The municipality of a large city has a stock of DVDs that it offers for rental to users of the various media libraries in this city. Among the DVDs removed, some are defective, others are not. Among the $6\%$ of defective DVDs in the entire stock, $98\%$ are removed. It is also admitted that among the non-defective DVDs, $92\%$ are kept in stock; the others are removed.
A DVD is chosen at random from the municipality's stock. Consider the following events:
  • $D$: ``the DVD is defective'';
  • $R$: ``the DVD is removed from stock''.
We denote by $\bar{D}$ and $\bar{R}$ the complementary events of events $D$ and $R$ respectively.
  1. Prove that the probability of event $R$ is 0.134.
  2. A charitable association contacts the municipality with the aim of recovering all DVDs that are removed from stock. A city official then claims that among these removed DVDs, more than half are composed of defective DVDs. Is this claim true?
The municipality of a large city has a stock of DVDs that it offers for rental to users of the various media libraries in this city. Among the DVDs removed, some are defective, others are not. Among the $6\%$ of defective DVDs in the entire stock, $98\%$ are removed. It is also admitted that among the non-defective DVDs, $92\%$ are kept in stock; the others are removed.

A DVD is chosen at random from the municipality's stock. Consider the following events:
\begin{itemize}
  \item $D$: ``the DVD is defective'';
  \item $R$: ``the DVD is removed from stock''.
\end{itemize}
We denote by $\bar{D}$ and $\bar{R}$ the complementary events of events $D$ and $R$ respectively.

\begin{enumerate}
  \item Prove that the probability of event $R$ is 0.134.
  \item A charitable association contacts the municipality with the aim of recovering all DVDs that are removed from stock. A city official then claims that among these removed DVDs, more than half are composed of defective DVDs. Is this claim true?
\end{enumerate}