Let $\Omega$ be the sample space and $\mathrm{A \subseteq \Omega}$ be an event.
Given below are two statements :
(S1) : If P(A) = 0, then A = $\phi$
(S2) : If P(A) = 1, then A = $\Omega$
Then :
Solution
$\Omega=$ sample space<br/><br/>
$\mathrm{A}=$ be an event<br/><br/>
$ \Omega$ = A wire of length 1 which starts at point 0 and ends at point 1 on the coordinate axis = $[0,1]$<br/><br/>
$\mathrm{A}=\left\{\frac{1}{2}\right\}$ = Selecting a point on the wire which is at $\left\{\frac{1} {2}\right\}$ or 0.5
<br/><br/>As wire is an 1-D object so from geometrical probability
<br/><br/>$P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
<br/><br/>Here total length of wire = 1 unit
<br/><br/>and point has zero length so point A at $\left\{\frac{1} {2}\right\}$ or 0.5 has length = 0.
<br/><br/>$\therefore$ Favorable length = 0
<br/><br/>
$\therefore$ $\mathrm{P}(\mathrm{A})=0 {\text { but }} \mathrm{A} \neq \phi$
<br/><br/>Now $\overline{\mathrm{A}}$ = $[0,1]$ - $\left\{\frac{1} {2}\right\}$
<br/><br/>So, length of $\overline{\mathrm{A}}$ = Length of entire wire - Length of point A = 1
<br/><br/>
$\therefore$ $\mathrm{P}(\overline{\mathrm{A}})=1 {\text { but }} \overline{\mathrm{A}} \neq \Omega$.<br/><br/>
Then both statements are false.
<br/><br/><b>Attention :</b> According to NTA option A is correct. Which is wrong. That is proven here using geometrical probability.
<br/><br/><b>Note :</b>
<br/><br/>Geometrical probability :
<br/><br/>1. For 1-D object, $P(A)=\frac{\text { Favourable Length }}{\text { Total Length }}$
<br/><br/>2. For 2-D object, $P(A)=\frac{\text { Favourable Area }}{\text { Total Area }}$
<br/><br/>3. For 2-D object, $P(A)=\frac{\text { Favourable volume }}{\text { Total volume }}$
About this question
Subject: Mathematics · Chapter: Probability · Topic: Classical and Axiomatic Probability
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