Answer to Question #282499 in Statistics and Probability for Sabeeh

Question

There are four red, three green, and five blue discs. Find the probability that the two discs of same color are drawn out

Answer 1

$$4+3+5=12$$

$$P(R,R)=\dfrac{4}{12}\cdot\dfrac{3}{11}=\dfrac{1}{11}$$

$$P(G,G)=\dfrac{3}{12}\cdot\dfrac{2}{11}=\dfrac{1}{22}$$

$$P(B,B)=\dfrac{5}{12}\cdot\dfrac{4}{11}=\dfrac{5}{33}$$

$$P(2\ same)=P(R,R)+P(G,G)+P(B, B)$$

$$=\dfrac{1}{11}+\dfrac{1}{22}+\dfrac{5}{33}=\dfrac{19}{66}$$