Question

A bag contains $3$ red and $3$ white balls. Two balls are drawn one by one. The probability that they are of different colours is.

• A. $\frac{3}{10}$
• B. $\frac{2}{5}$
• C. $\frac{3}{5}$
• D. None of these

Answer 1

Answer: (C)

$\frac{3}{5}$

Answer 2

Let $A \equiv$ event that drawn ball is red
$B \equiv$ event that drawn ball is white
Then $AB$ and $BA$ are two disjoint cases of the given event Therefore, $P ( AB + BA )= P ( AB )+ P ( BA )$
$=P(A) P\left(\frac{B}{A}\right)+P(B) P\left(\frac{A}{B}\right)$
$=\frac{3}{6} \cdot \frac{3}{5}+\frac{3}{6} \cdot \frac{3}{5}$
$=\frac{3}{5}$