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A speaks the truth in 70% cases and B speaks the truth in 84% cases. What is the probability that they contradict each other on a statement?
Question

A speaks the truth in 70% cases and B speaks the truth in 84% cases. What is the probability that they contradict each other on a statement?

A.

0.154

B.

0.636

C.

0.140

D.

0.364

Correct option is D

We are given: A speaks the truth with probability P(AT)=0.70, so lies with probability P(AL)=10.70=0.30 B speaks the truth with probability P(BT)=0.84, so lies with probability P(BL)=10.84=0.16We are to find the probability that A and B contradict each other, i.e., one tells the truth and the other lies.This happens in two mutually exclusive cases:1. A tells the truth and B lies:P(ATBL)=P(AT)P(BL)=0.700.16=0.1122. A lies and B tells the truth:P(ALBT)=P(AL)P(BT)=0.300.84=0.252Total probability that A and B contradict each other:P(contradiction)=0.112+0.252=0.364\begin{aligned}&\text{We are given:} \\[5pt]&\bullet\ \text{A speaks the truth with probability } P(A_T) = 0.70,\ \text{so lies with probability } P(A_L) = 1 - 0.70 = 0.30 \\[5pt]&\bullet\ \text{B speaks the truth with probability } P(B_T) = 0.84,\ \text{so lies with probability } P(B_L) = 1 - 0.84 = 0.16 \\[15pt]&\textbf{We are to find the probability that A and B contradict each other, i.e., one tells the truth and the other lies.} \\[8pt]&\text{This happens in two mutually exclusive cases:} \\[8pt]&1.\ \text{A tells the truth and B lies:} \\&P(A_T \cap B_L) = P(A_T) \cdot P(B_L) = 0.70 \cdot 0.16 = 0.112 \\[10pt]&2.\ \text{A lies and B tells the truth:} \\&P(A_L \cap B_T) = P(A_L) \cdot P(B_T) = 0.30 \cdot 0.84 = 0.252 \\[15pt]&\text{Total probability that A and B contradict each other:} \\&P(\text{contradiction}) = 0.112 + 0.252 = {0.364}\end{aligned}​​

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