Question

An urn contains five red marbles, four green marbles, and three blue marbles. If one marble is drawn at random, what is the probability that it is either a green marble or a blue marble?

Answer 1

Hi

first thing to do is to count how many marbles you have

so :  5 red, 4 green, 3 blue  =  5+4+3 = 12  

probability  of  green :    4/12

                         blue   :     3/12  

Probability of  either  green or blue  :  4/12 +3/12 = 7/12