probability

 

A jar contains two red marbles, three green marbles, ten white marbles and no other marbles. Two marbles are randomly drawn from this jar without replacement. What is the probability that these two marbles drawn will both be red?     

 

red marbles in jar   =   2     

all marbles in jar    =  15     

chance of 1st drawn marble being red  =  2 / 15     

 

red marbles in jar   =   1     

all marbles in jar    =  14     

chance of 2nd drawn marble being red  =  1 / 14     

 

chance of both things happening  =  (2 / 15) • (1 / 14)  =  2 / 210     

 

                                                                    reduces to  =  1 / 105     

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