
L'intervalle de confiance est :
\[
I=\intervFF{0,535-\dfrac{1}{\sqrt{n}}}{0,535+\dfrac{1}{\sqrt{n}}}=\intervFF{0,51}{0,56}.
\]
Donc
\begin{align*}
0,535-\dfrac{1}{\sqrt{n}}=0,51 
& \iff 0,535-0,51 = \dfrac{1}{\sqrt{n}}\\
& \iff 0,025 = \dfrac{1}{\sqrt{n}}\\
& \iff \dfrac{1}{0,025}=\sqrt{n}\\
& \iff 40 = \sqrt{n}\\
& \iff 40^2 = n\\
& \iff \uline{n=\numprint{1600}}.
\end{align*}
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