Question

A speaks truth in 75% of cases and B in 80% of cases. In what percent of cases are they likely to contradict each other in narrating the same event?

• A. $20\%$
• B. $25\%$
• C. $30\%$
• D. $35\%$

Answer 1

The correct option is D $35\%$

Different possible cases of contradiction,
A speaks truth and B does not speaks truth.
Or, A does not speak truth and B speaks truth.
$=(\frac{3}{4}\times \frac{1}{5})+(\frac{1}{4}\times \frac{4}{5})=\frac{3}{20}+\frac{4}{20}=\frac{7}{20}=35\%$