Question

An urn contains 4 red and 7 black balls. Two balls are drawn at random with replacement. Find the probability of getting 2 blue balls. 

Answer 1

\[\text{ Total balls = 4 red balls + 7 blue balls = 11 balls } \] 

\[ P\left( 2 \text{ blue balls } \right) = P\left( \text{ first ball is blue } \right) \times P\left( \text{ second ball is blue } \right)\]
\[ = \frac{7}{11} \times \frac{7}{11}\]
\[ = \frac{49}{121}\]