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If a person A speaks the truth in 80% cases and the person B speaks the truth in 75% cases, then the probability that they contradict each other in a statement is

Solution

✅ Correct Option: 4

Person A speaks the truth in 80% of cases, so A speaks the truth with probability 45\frac{4}{5} and lies with probability 15\frac{1}{5}.

Person B speaks the truth in 75% of cases, so B speaks the truth with probability 34\frac{3}{4} and lies with probability 14\frac{1}{4}.

Two people contradict each other when one tells the truth and the other lies.


A tells the truth and B lies:

Probability =45×14= \frac{4}{5} \times \frac{1}{4}

=420= \frac{4}{20}

=15= \frac{1}{5}


A lies and B tells the truth:

Probability =15×34= \frac{1}{5} \times \frac{3}{4}

=320= \frac{3}{20}


Total probability of contradiction:

=15+320= \frac{1}{5} + \frac{3}{20}

=420+320= \frac{4}{20} + \frac{3}{20}

=720= \frac{7}{20}

Therefore, the probability that they contradict each other is 720\frac{7}{20}.

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