A box contains one red marble two green marbles and seven bl

A box contains one red marble, two green marbles and seven blue marbles. When two marbles are selected randomly, find the probability that both marbles have the same color. one of the marbles is red.

Solution

a)

P(both marbles are red) = 0

P(both marbles are green) = 2C2/10C2 = 2/10*9 = 1/45[C is the choose function]

P(both marbles are blue) = 7C2/10C2 = 21/45

P(both marbles have same color) = 1/45+ 21/45 = 22/45

b)

P (one of the marbles is red) = 1C1 * 9C1/ 10 C2 = 9/45 = 1/5

comment if something not clear