Question
Probability of solving specific problem independently by A and B are $\frac{1}{2}$ and $\frac{1}{3}$ respectively. If both try to solve the problem independently, find the probability that, exactly one of them solve the problem.

Answer

$A$ and $B$ are independently try to solve problem with probability
$\begin{array}{l}
P(A)=\frac{1}{2} \\
P(B)=\frac{1}{3}
\end{array}$
Which are independent events.
$\therefore P(A \cap B)=P(A) \cdot P(B)$
$\rightarrow$ Exactly one of them solves the problem
$\begin{array}{l}
=P\left(A \cap B^{\prime}\right)+P\left(A^{\prime} \cap B\right) \\
=P(A)-P(A \cap B)+P(B)-P(A \cap B) \\
=P(A)+P(B)-2 P(A) P(B) \\
=\frac{1}{2}+\frac{1}{3}-2 \times \frac{1}{2} \times \frac{1}{3} \\
=\frac{1}{2}+\frac{1}{3}-\frac{1}{3} \\
=\frac{1}{2}
\end{array}$

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