An urn contains 7 red and 4 blue balls. Two balls redrawn at random with replacement.  Find the probability of getting 2 red balls 2 blue balls one red and one blue ball.

Explanation

(i) `P(2` red balls `)=frac{7}{11} times frac{7}{11}`


`=frac{49}{121}`


(ii) `P(2` blue balls `)=frac{4}{11} times frac{4}{11}`


`=frac{16}{121}`


(iii ) P( one red ball and one blue ball )=P( blue ball followed by red ball )+P( red ball followed by blue ball )
`=frac{4}{11} times frac{7}{11}+frac{7}{11} times frac{4}{11}`


`=frac{28}{121}+frac{28}{121}`


`=frac{56}{121}`